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.