A heavily armed man and woman in their 20s have died in a shootout with police after killing 14 people at a Christmas party in California.
Police identified the pair as Syed Farook, a 28-year-old US citizen who worked for the local county, and Tashfeen Malik, 27, whose nationality is unknown. They said the suspects were either married or engaged.
Jarrod Burguan, San Bernardino's police chief, confirmed both were dead and that police no longer believed a third suspect mentioned earlier was at large.
The shooters targeted a year-end party taking place at a social services centre in San Bernardino, about an hour's drive east of Los Angeles, killing 14 people and wounding 17.
"We don't have the motive at this point," the police chief said. "We have not ruled out terrorism."
The massacre drew an angry response from President Barack Obama, who once again urged congress to pass tougher gun control measures to stem America's epidemic of gun violence.
According to Burguan, Farook was an environmental inspector who had worked for the county health department for five years.
He and Malik were dressed in military-style gear and carried assault weapons as they burst into the auditorium where the bloodbath took place. The hall was let out for the holiday party by the Inland Regional Center for the disabled.
Burguan said Farook had attended the Christmas party organised by the health department and left after an apparent dispute, only to return a short time later with Malik, armed with assault rifles and semi-automatic handguns.
"Based upon how they were equipped, there had to be some degree of planning that went into this," he said.
"I don't think they just ran home and put on these tactical clothes, grabbed guns and came back on a spur of the moment thing."
He said the attackers left explosive devices behind and authorities were only able to access the scene of the crime several hours after the shooting.
FBI agents in the early evening raided an apartment in the nearby town of Redlands, where the two suspects were seen before the police chase that ended in a shootout a few miles from the Inland Regional Center.
The California chapter of the Council on American-Islamic Relations denounced the killings. Farook's brother-in-law, Farhan Khan, said he had no clue what prompted the carnage.
"I am in shock that something like this could happen," a visibly shaken Khan told a press conference.
The Los Angeles Times quoted some of Farook's co-workers as saying he had previously travelled to Saudi Arabia and returned with a new wife. The couple had a six-month-old daughter and appeared to be "living the American dream", Patrick Baccari, a co-worker who shared a cubicle with Farook, told the paper.
Witnesses at the California scene recounted barricading themselves in offices and hiding as the sound of gunfire erupted.
Mark Stutte said his daughter was attending the party organised by the county's public health department and called him terrified while hiding in a restroom as gunshots rang out in the background.
"It was really, really super scary," he told local TV, as he wept. "I'm far away. I couldn't do anything for her."
The local San Bernardino newspaper The Sun identified one of the victims as Jennifer Stevens who underwent surgery for a gunshot wound to the abdomen and was expected to recover.
It said Stevens, 22, had texted her mother right after the shooting saying: "Mom, I'm at work, I've been shot."
Obama, who just last week made a plea for action on gun control after three people were killed at a family planning centre in Colorado, voiced his anger once more.
"The one thing we do know is that we have a pattern now of mass shootings in this country that has no parallel anywhere else in the world," he told CBS News.
"There are some steps we could take, not to eliminate every one of these mass shootings, but to improve the odds that they don't happen as frequently."
According to the site Mass Shooting Tracker, the latest attack brings to 352 the number of mass shootings in the US so far this year. A mass shooting is defined as four or more people shot in one incident.
