Islamic State terrorists have claimed responsibility for the shootings in California that killed 14 people. The Aamaq news agency, which supports ISIS, said on its website on Friday that followers of the Islamist militant group had carried out Wednesday's attack.
The FBI also said they are investigating the incident as an 'act of terrorism'.
American-born Syed Farook, 28, carried out the attack with his wife, Tashfeen Malik, 27, after storming out of the office Christmas party.
The pair, who are Muslims, donned dark, tactical gear and masks, arming themselves with high-powered assault rifles and handguns, police said.
After entering the Inland Regional Centre in San Bernardino, where Farook worked, the murderous duo sprayed bullets inside a conference room.
During the attack, 14 people were killed almost instantly while 17 others were injured. Doctors said 10 of the wounded were in a critical condition.
Three explosive devices, which were connected to one another, were found inside the building and later detonated by a bomb squad.
Fours hours after the killings the couple were shot dead during a fierce gun battle with police after they were tailed from their home in nearby Redlands.
