Islamic State said on Saturday that the married couple who killed 14 people in a mass shooting in California which the U.S. authorities are investigating as an act of terrorism were its followers.
The militant group made the statement in an online radio broadcast three days after U.S.-born Syed Rizwan Farook, 28, and his wife Tashfeen Malik, 29, from Pakistan, attacked a holiday party for civil servants in San Bernardino, about 60 miles (100 km) east of Los Angeles.
The pair were killed two hours later in a shootout with police.
Officials with the Federal Bureau of Investigation, which is leading the probe into the shooting, said Malik and her husband appeared to have been inspired by foreign militant groups but there was no sign they had worked with any of them or that Islamic State even knew who they were.
"It is entirely possible that these two attackers were radicalized to commit this act of terror," U.S. President Barack Obama said in a radio address on Saturday. "If so, it would underscore a threat we've been focused on for years, the danger of people succumbing to violent extremist ideologies."
If the Dec. 2 mass shooting proves to have been the work of people inspired by Islamist militants, it would mark the deadliest such attack in the United States since Sept. 11, 2001.
Islamic State also claimed responsibility for a Nov. 13 series of attacks in Paris in which gunmen and suicide bombers killed 130 people.
"Two followers of Islamic State attacked several days ago a center in San Bernardino in California," the group's daily online radio broadcast al-Bayan said on Saturday.
An English-language version of the broadcast was later released calling the attackers "soldiers" of Islamic State, rather than "followers" as in the original Arabic version. It was unclear if the English version was claiming them as members, or why there was an inconsistency.
The broadcast came a day after Facebook confirmed that comments praising Islamic State were posted around the time of the mass shooting to an account on the social media website established by Malik under an alias.
However, it was uncertain whether the comments were posted by Malik herself or someone with access to her page.
The couple had two assault-style rifles, two semi-automatic handguns, 6,100 rounds of ammunition and 12 pipe bombs in their home or with them when they were killed, officials said. The large arsenal could indicate they were planning further attacks.
The attack sparked a new round of the firearms debate with Obama and the New York Times calling for new limits on gun ownership. Many pro-gun voices, including some Republican contenders for the White House, said the new laws would not have stopped the rampage.
"It's another tragic reminder that here in America it's way too easy for dangerous people to get their hands on a gun," said Obama.
The New York Times, in its first front-page editorial since 1920, said it was "a moral outrage and a national disgrace" that the sort of firearms used in the attack were readily available.
"These are weapons of war, barely modified and deliberately marketed as tools of macho vigilantism and even insurrection," the newspaper said.
The newspaper's publisher, Arthur Sulzberger Jr, said that the editorial was intended "to deliver a strong and visible statement of frustration and anguish about our country's inability to come to terms with the scourge of guns."
But Republican White House frontrunner Donald Trump dismissed the New York Times' call for action.
"People in this country and the world need protection," Trump told reporters in Iowa before a campaign event. "If you look at Paris, they didn't have guns and they were slaughtered. If you look at California, they didn't have guns and they were slaughtered."
U.S. Senator Marco Rubio of Florida, a Republican also seeking the presidential nomination, said restrictions on guns would not have stopped the California attack or other mass shootings, including recent attacks on an Oregon college and a Planned Parenthood health clinic in Colorado.
Citing an unnamed federal law enforcement official, the Los Angeles Times reported that Farook had "some kind" of contact with people from the Nusra Front and the radical Shabab group in Somalia, though the nature of that contact was unclear.
FBI Director James Comey said on Friday that the investigation suggested the attackers had possibly been inspired by "foreign terrorist organizations" but added there was no evidence they were part of a larger group.
Farook family attorneys on Friday denied there was any evidence that either the husband or wife harbored extremist views.
She spoke broken English and her primary language was Urdu, Farook family attorney David Chesley said, adding: "She was very conservative." They said Farook, too, largely kept to himself, had few friends and said co-workers sometimes made fun of his beard.
Pakistani intelligence officials have contacted Malik's family in her homeland as part of the investigation, a family member said.