California shooting investigated as potential terrorism: FBI chief

US Federal Bureau of Investigation (FBI) chief James Comey said Friday that shooting in Californian City San Bernardino was being investigated as potential terrorism, but there was "no indication" suggesting killers of the holiday party carnage had been part of any terrorist group.

"The investigation so far has delivered indications of radicalization by the killers and of potential inspiration by foreign terrorist organisations," Xinhua quoted Comey as saying.

However, Comey said so far there was no indication that pointed to the husband-and-wife shooters' affiliation to any group.

"We have no indication that these killers are part of an organised larger group or form part of a cell. There is no indication that they are part of a network," said Comey.

The couple shot down 14 people Wednesday at a Southern California social services center and injuried several. According to local police, "some degree of planning" was involved in the shooting spree.

The two suspects, 28-year-old US citizen Syed Farook and his 27-year-old wife Tashfeen Malik, had 1,600 rifle and 9-millimeter rounds of ammunition when they were killed, and 2,000 9-millimeter rounds and 2,500 0.223 rifle rounds at home, as well as 12 pipe bombs and tools to make bombs, according to police.

And those do not include the hundreds of rounds they fired in the shooting and gunfire with police.

It was revealed on Friday that the wife had pledged allegiance to the Islamic State (IS) on social media.