President Barack Obama says the US “will not be terrorised” by Wednesday’s mass shootings in San Bernardino, California.
“We are strong. And we are resilient,” he said in his weekly radio address, adding that it was “entirely possible” the two attackers had been radicalised.
Syed Rizwan Farook, 28, and his wife Tashfeen Malik, 29, killed 14 people before being shot dead by police.
The FBI is investigating the shootings as an “act of terrorism”.
The Islamic State militant group on Saturday hailed the attack, saying it had been carried out by “two supporters of the Islamic State”.
The statement, carried by IS’s al-Bayan radio, gave no indication that the group had any involvement in planning the shootings at the Inland Regional Center social services agency.
“We know that Isil [IS] and other terrorist groups are actively encouraging people – around the world and in our country – to commit terrible acts of violence, oftentimes as lone wolf actors,” Mr Obama said in his address.
“All of us – government, law enforcement, communities, faith leaders – need to work together to prevent people from falling victim to these hateful ideologies.”
Later, the White House said Mr Obama had been updated on the investigation by senior officials, including FBI Director James Comey, who confirmed there was so far no indication that the killers were part of an “organised group or formed part of a broader terrorist cell”.
The FBI is also investigating reports that Malik had posted a message on Facebook pledging allegiance to IS.
Farook, who worked for the local health department, and Malik opened fire on an office Christmas party, killing 14 people and wounding 21.
FBI officers are trying to recover data from two mobile phones that were found crushed in a waste bin near the scene.
On Friday lawyers representing the attackers’ family said the relatives were “in complete shock” and that they had no idea the two had been capable of such an attack.
Syed Rizwan Farook’s sister, Saira Khan, told CBS News: “I can never imagine my brother or my sister-in-law doing something like this, especially because they were happily married, they had a beautiful six-month-old daughter.”
Tashfeen Malik was born in Pakistan and lived for 20 years in Saudi Arabia before moving back to her native country to go to university.
She and Farook, a US national, met on Muslim dating websites, the New York Times quotes officials as saying. The new couple spent about a week in Saudi Arabia last year, before returning to the US together.
She was granted a visa allowing people to enter the US to marry American citizens. Mr Chesley said Malik was very conservative. She did not interact with male family members and wore a burka, he said.