Islamic State said on Saturday, December 5, that a married couple who killed 14 people in California in an attack the FBI is investigating as an "act of terrorism" were followers of the militant group based in Syria and Iraq, Reuters reports.

The group's declaration, in an online radio broadcast comes three days after U.S.-born Syed Rizwan Farook, 28, and his spouse, Tashfeen Malik, 29, a native of Pakistan, carried out the attack on a holiday party for civil servants in San Bernardino, about 60 miles (100 km) east of Los Angeles.

The two died hours later in a shootout with police.

U.S. government sources have said Malik and her husband may have been inspired by Islamic State, but there was no evidence the attack was directed by the militant group or that the organization even knew who they were. The party the couple attacked was for workers in the same local government agency that employed Farook.

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.

CNN and other news media outlets reported the Facebook posts on Malik's page included a pledge of allegiance to Islamic State leader Abu Bakr al-Baghdadi.