A mass shooting by a married couple that left 14 people dead in California is being investigated as an act of terrorism, the FBI says.
The pair undertook “extensive planning” before carrying out the assault, said FBI spokesman David Bowdich.
Tashfeen Malik, 27, and her husband Syed Rizwan Farook, 28, died in a shootout with police after the killings at San Bernardino, east of Los Angeles.
It follows reports that Malik had pledged allegiance to Islamic State.
Malik is reported to have posted a message on Facebook in support of IS leader Abu Bakr al-Baghdadi under a different name. The post has since been removed.
In another development on Friday, the couple’s landlord opened their apartment to the media, prompting journalists and camera crews to rush in and survey the scene.
There has been strong criticism on social media for several outlets including the BBC, but the FBI had released the residence to the landlord before he let journalists in.
After Wednesday’s attack at the Inland Regional Center social services agency, bomb equipment, weapons and thousands of rounds of ammunition were found in the couple’s home.
Mr Bowdich said the authorities were trying to recover data from two mobile phones found crushed in a waste bin near the shooting scene.
He said “telephonic connections” had been established between the couple and other people of interest to the authorities.
The New York Times reported that there was no evidence that IS had directed the couple in the attack.
“At this point we believe they were more self-radicalised and inspired by the group than actually told to do the shooting,” the newspaper quoted an official as saying.
Investigators are also said to be following up a report that Farook had argued with a colleague at work who denounced the “inherent dangers of Islam”.
Malik was born in Pakistan and had recently lived in Saudi Arabia.
Intelligence officials in Pakistan have contacted relatives there, a family member quoted by Reuters said.
Farook, who worked as an inspector for the city’s environmental health department, was the son of Pakistani immigrants and born in the US state of Illinois.
Police said between 75 and 80 people were attending a party at the centre when the shooting began.