CAIRO — When a new bout of fighting between rival militias engulfed the Libyan capital in recent days, badly shaking the fragile United Nations-backed government, some combatants picked up rifles and rocket launchers and headed into the streets.
Others logged on to Facebook.
As rockets rained on parts of Tripoli, hitting a hotel popular with foreigners and forcing the airport to close, and 400 prisoners escaped from a jail, a parallel battle unfolded online. On their Facebook pages, rival groups issued boasts, taunts and chilling threats — one vowing to "purify" Libya of its opponents.
Some "keyboard warriors," as Facebook partisans are known in Libya, posted fake news or hateful comments. Others offered battlefield guidance. On one discussion page on Thursday, a user posted maps and coordinates to help target her side's bombs at a rival's air base.
"From the traffic light at Wadi al Rabi, it is exactly 18 kilometers to the runway, which means it can be targeted by a 130 mm artillery," the user, who went by the handle Narjis Ly, wrote on Facebook. "The coordinates are attached in the photo below."
Social media enjoys outsize influence in Libya, a sparsely populated yet violently fractured country that is torn by a plethora of armed groups vying for territory and legitimacy. They battle for dominance on the streets and on smartphones.
But Facebook, by far the most popular platform, doesn't just mirror the chaos — it can act as a force multiplier.
Armed groups use Facebook to find opponents and critics, some of whom have later been detained, killed or forced into exile, according to human rights groups and Libyan activists. Swaggering commanders boast of their battlefield exploits and fancy vacations, or rally supporters by sowing division and ethnic hatred. Forged documents circulate widely, often with the goal of undermining Libya's few surviving national institutions, notably its Central Bank.
Facebook is coming under scrutiny globally for how its platform amplifies political manipulation and violence. In July, the company began culling misinformation from its pages in response to episodes in Sri Lanka, Myanmar and India where online rumors led to real-life violence against ethnic minorities.
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On Wednesday, Facebook's chief operating officer, Sheryl Sandberg, will defend the company's efforts to limit disinformation and hate speech before the Senate Intelligence Committee, where she will testify along with Jack Dorsey, Twitter's chief executive.
Facebook insists it is assiduously policing its raucous Libyan platform. It employs teams of Arabic-speaking content reviewers to enforce its policies, is developing artificial intelligence to pre-emptively remove prohibited content, and partners with local organizations and international human rights groups to better understand the country. A spokeswoman said: "We also don't allow organizations or individuals engaged in human trafficking or organized violence to maintain a presence on Facebook."
Still, illegal activity is rife on Libyan Facebook.
The New York Times found evidence of military-grade weapons being openly traded, despite the company's policies forbidding such commerce. Human traffickers advertise their success in helping illegal migrants reach Europe by sea, and use their pages to drum up more business. Practically every armed group in Libya, and even some of their detention centers, have their own Facebook page.
Facebook removed several pages and posts after The New York Times flagged them to the spokeswoman on Sunday. But others remained.
"The most dangerous, dirty war is now being waged on social media and some other media platforms," Mahmud Shammam, a former information minister, said last week as fighting ripped through the Tripoli suburbs. "Lying, falsifying, misleading and mixing facts. Electronic armies are owned by everyone, and used by everyone without exception. It is the most deadly war."
Mr. Shammam made his declaration, naturally, on Facebook.
Facebook helped Libyans unite in 2011 to oust Col. Muammar el-Qaddafi, who for decades had forbidden people to buy fax machines or even printers without official permission.
Even then, the platform was prone to abuse.
A vicious hate campaign directed at suspected Qaddafi supporters, and which was fanned by incendiary social media posts, led to African migrants being jailed or lynched, and caused all 30,000 residents of a town called Tawergha to flee for their lives. Today, most Tawerghans live in refugee camps.
"The social media echo chamber played out in deadly ways for them," said Fred Abrahams, an associate director at Human Rights Watch.
Facebook's influence today is largely a product of Libya's dysfunction. The country has no central authority and most of its TV stations and newspapers are tied to armed groups, political factions or foreign powers like Qatar and the United Arab Emirates.
Many Libyans spend long hours stranded inside their homes because it can be dangerous to go out. The electricity can be off for 12 hours a day. So they turn to Facebook to find out what's going on.
"The phone might be the only thing that is working," said Jalel Harchaoui, a Paris-based analyst with North Africa Risk Consulting. "People are traumatized after the years of fake news under Qaddafi. They thirst for truth."
Some 181 million people use Facebook every month across the Middle East and North Africa, the Facebook spokeswoman said. She replied to questions by email on condition of anonymity in line with Facebook policy, which the company said was mainly for security reasons. For Libya's armed factions, that reach makes the platform a powerful tool for propaganda and repression.
In the eastern city of Benghazi, which is dominated by the strongman Gen. Khalifa Hifter, a special online unit affiliated with his militia, the Libyan National Army, scours Facebook for signs of dissent or for suspected Islamists. Some have been arrested and jailed, and others forced to flee the city, according to human rights groups.
There are similar pressures in Tripoli, where the Special Deterrence Force, a militia led by a conservative religious commander, Abdulrauf Kara, patrols Facebook with a moralizing zeal reminiscent of Saudi Arabia's once-feared religious police.
Last year his militia detained 20 participants in a Libyan version of Comic-Con, the comic book conference. The militants said they were outraged by photos on Facebook showing young Libyans dressed as characters like Spider-Man and the Joker. Some detainees said they were beaten in custody.
In August 2017, a writer named Leila Moghrabi was hit by a blizzard of Facebook attacks over a collection of short stories and poetry she edited. "I wish you get killed, not arrested," read one typical message. Three Muslim clerics denounced Ms. Moghrabi in thundering sermons that circulated on Facebook; next came word that the Special Deterrence Force was coming to arrest her.
She leapt into a car with her husband and children and drove to Tunisia, where they live in exile. "We literally left everything behind," she said by phone.
Others never made it to the border. Jabar Zain, a 30-year-old activist who was prominent on Facebook, has not been seen since he was abducted by a militia in September 2016, according to Amnesty International, which said he was targeted because of statements he made on Facebook. Amnesty has documented several such cases.
In 2014, suspected Islamists in Benghazi shot dead two secular teenage activists, Tawfik Bensoud and Sami al-Kwuafi, after their names appeared on a hit list that circulated on Facebook.
The fighting in Tripoli over the past week was the worst in years, leaving at least 47 people dead, including children, and over 130 wounded, according to health officials. At least 400 prisoners escaped from a jail on Sunday after inmates overpowered guards. The chaos poses a growing threat to the United Nations-backed unity government, which has declared a state of emergency in the capital.
Online boasts and threats foreshadowed the fighting.
Although Tripoli seemed calm this year, public unease grew toward the four big militias that control the city under the umbrella of the fragile unity government, which is headed by Fayez Seraj. The militia commanders are widely viewed as unaccountable and corrupt, using their access to the Central Bank to buy United States dollars at the official rate, which is five times cheaper than the street price.
One commander, Haitham Tajouri, drew attention by posting photos to Facebook flaunting his lavish lifestyle — foreign vacations, designer suits and an armored S.U.V. — at a time when many Libyans were wallowing in economic hardship.
Such ostentatious displays helped fuel resentments among rival groups seeking to share in the pie. They boiled over last week when a militia known as Kaniyat from a town called Tarhouna, 45 miles southeast of Tripoli, launched an assault on the capital.
As Kaniyat's fighters engaged in artillery battles in the southern suburbs, it sought to tap into public anger by denouncing its rivals as the "Islamic State of public money" and promising to "cleanse" them from Libya.
Libya's factions are motivated by more than what they see on Facebook, said Mr. Harchaoui, the analyst. But, he added, "it can be the final straw."
On Monday afternoon, Facebook suddenly went down in Tripoli. The local internet provider, Libya Telecom and Technology, which insisted it had not blocked Facebook, said it was investigating.
Facebook employs Arabic-language reviewers who weed out illegal and forbidden content on its Libyan pages — part of a global team that works in over 50 languages, the company says.
"We work hard to keep Facebook safe and to prevent people from using our tools to spread hate or incite violence," the spokeswoman said. The company engages with academics and civil society groups to "better understand local issues and context so we can take more effective action against bad actors on Facebook," she added.
But Libyans are adept at circumventing such controls. Users often take screenshots of contentious posts, and redistribute them as images if the original text is removed by Facebook's moderators.
Although Facebook prohibits firearms trading between individuals, numerous pages present themselves as online weapons bazaars. On the page "Libya's Weapons Market," sellers advertise machine guns, antiaircraft guns and artillery shells. Last month, for instance, one user posted an image of a Russian PM machine gun. "Message me if you are serious about purchasing," the message said.
On Monday, Facebook said it had removed those posts, as well as two other pages cited by The New York Times that advertised the services of human traffickers sending illegal migrants by boat to Europe. "We are investigating to understand why we didn't take action sooner," the spokeswoman said.
Facebook has developed tools that scan for prohibited content, which human moderators can then remove. These programs flagged 85 percent of the "violent content" that was removed or given a warning label in the first three months of 2018, the spokeswoman said. But the programs struggle to identify subtler violations such as hate speech or violent threats, which are mostly reported by everyday users. This can make removal slow, particularly in areas where locals may be less inclined to report the posts.
In 2011, Facebook reflected the "extraordinary" opening up of Libyan society after four decades of dictatorship under Colonel Qaddafi, said Mary Fitzgerald, an independent researcher on Libya. "Everyone was on Facebook. There was a very rambunctious conversation, and a lot of debate."
But as the years went on, the people driving the conflict began to "talk about how social media is one of their most important weapons," she said. That bred a deep ambivalence among many Libyans toward the media they consume so voraciously.
"So many times over the past seven years," she added, "I heard people say that if we could just shut down Facebook for a day, half of the country's problems would be solved."