BEIRUT - Islamic State said in an online radio broadcast on Saturday that two followers of the Islamist militant group had carried out Wednesday's attack on a social services agency party in California where 14 people were killed.

"Two followers of Islamic State attacked several days ago a centre in San Bernadino in California, opening fire inside the centre, leading to the deaths of 14 people and wounding more than 20 others," the group's daily broadcast al-Bayan said, giving information already widely reported.

A news agency that supports Islamic State, which controls large parts of Syria and Iraq, said on Friday the attackers were followers of the group. The broadcast was the first claim from the group itself.

U.S. government sources have said there is no evidence the attack was directed by the militant group, or that it even knew who the attackers were.

The FBI said it lacked evidence that the married couple who carried out the attack belonged to a larger organization of extremists.

The Los Angeles Times cited a federal law enforcement source in reporting that the husband had contact with at least two militant groups overseas, including the al Qaeda-affiliated Nusra Front in Syria.