The European Union's foreign policy chief, Catherine Ashton, said Friday that the bloc needs to consider sanctions such as travel restrictions and an asset freeze against Libya to achieve a halt to the violence there and move toward democracy.
NATO's main decision-making body also planned to meet in emergency session Friday to consider the deteriorating situation, although Secretary-General Anders Fogh Rasmussen has said the alliance has no intention of intervening in the North African nation.
The U.N.'s top human rights official, Navi Pillay, meanwhile, said there are reports of mass killings of thousands in Libya that should spur the international community to "step in vigorously" to end the crackdown against anti-government protesters.
Most of the eastern half of Libya has already broken away, and diplomats, ministers and even a high-ranking cousin have abandoned Gaddafi, who has ruled Libya for 41 years. He is still believed to be firmly in control only of the capital, some towns around it, the far desert south and parts of Libya's sparsely populated center.
Residents in several cities said the opposition had called on people to rally in demonstrations after Friday prayers.
Some Tripoli residents also reported receiving text messages on their cell phones urging them to go protest in the capital's central Green Square after Friday prayers. The plaza was the site of intense clashes earlier in the week between government supporters and protesters.
Gaddafi's crackdown -- the harshest by any Arab leader in the wave of protests that has swept the Middle East the past month -- has so far helped him maintain control of Tripoli, home to about a third of Libya's 6 million population. But the uprising has divided the country and raised the specter of civil war.
The New York-based Human Rights Watch has put the death toll in Libya at nearly 300, according to a partial count. Italy's Foreign Minister Franco Frattini said estimates of some 1,000 people killed were "credible."
In cities across the east, anti-Gaddafi forces rose up and overwhelmed government buildings and army bases, joined in many cases by local army units that defected. In those cities, tribal leaders, residents and military officers have formed local administrations, passing out weapons looted from the security forces' arsenals.
The rebels now control a swath of territory from the Egyptian border in the east, across nearly half Libya's 1,000-mile (1,600-kilometer) Mediterranean coast to the key oil port of Breqa, about 440 miles (710 kilometers) east of Tripoli.
A witness said police had disappeared from the streets and a committee had been formed to run things in Misrata, where pro-Gaddafi militiamen -- a mix of Libyans and foreign mercenaries -- battled with government opponents who had been guarding an airport outside the city. Seven people were killed in the fighting, according to a medical official.
"Now it is calm, but there are worries that the government is preparing lots of security forces and that there will be a massacre today," he said. "We are spread out all over the city and the youths are in control."
The witness, who like many residents and officials spoke on condition of anonymity for fear of reprisals, said a protest was planned later Friday in Misrata, Libya's third-largest city about 120 miles (200 kilometers) from the capital. He said a small group of youths might be dispatched to Tripoli after the opposition movement called for protesters to march on the capital, but the others had to stay behind to protect their city amid rumors the regime planned to attack again.
The worst bloodshed Thursday was in Zawiya, 30 miles (50 kilometers) west of the capital Tripoli. An army unit loyal to Gaddafi opened fire with automatic weapons on a mosque where residents -- some armed with hunting rifles for protection -- have been holding a sit-in to support protesters in the capital, a witness said.
The troops blasted the mosque's minaret with an anti-aircraft gun. A doctor at a field clinic set up at the mosque said he saw the bodies of 10 dead, shot in the head and chest, as well as around 150 wounded. A Libyan news website, Qureyna, put the death toll at 23 and said many of the wounded could not reach hospitals because of shooting by "security forces and mercenaries."
Zawiya, a key city close to an oil port and refineries, is the nearest population center to Tripoli to fall into the hands of the anti-Gaddafi rebellion that began Feb. 15. Hundreds have died in the unrest.
The upheaval in the OPEC nation has taken most of Libya's oil production of 1.6 million barrels a day off the market. Oil prices hovered above $98 a barrel Friday in Asia, backing away from a spike to $103 the day before amid signs the crisis in Libya may have cut crude supplies less that previously estimated.
Hours after the attack in Zawiya, Gaddafi called in to state TV and in a rambling speech expressed condolences for the dead but then angrily scolded the city's residents for siding with the uprising.
He blamed the revolt on al-Qaida leader Osama bin Laden and teenagers hopped up on hallucinogenic pillsgiven to them "in their coffee with milk, like Nescafe."
In another blow to the Libyan leader, a cousin who is one of his closest aides, Ahmed Gadhaf al-Dam, announced that he has defected to Egypt in protest against the regime's bloody crackdown, denouncing what he called "grave violations to human rights and human and international laws."
Gadhaf al-Dam is one of the highest level defections to hit the regime so far, after many ambassadors around the world, the justice minister and the interior minister all sided with the protesters. Gadhaf al-Dam belonged to Gaddafi's inner circle, served as his liaison with Egypt and frequently appeared by his side.