KAROR ESAN: The estranged relatives of Tashfeen Malik, a Pakistani woman accused of shooting dead 14 people in California, say she and her father seem to have abandoned the family's moderate Islam and became more radicalised during years they spent in Saudi Arabia.

Malik, with her husband Syed Rizwan Farook, 28, is accused of storming a gathering in San Bernardino, California, on Wednesday and opening fire in America's worst mass shooting in three years.

Investigators are treating Wednesday's attack as an "act of terrorism".

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Malik's killing spree has horrified her Pakistani relatives.

Her father cut off contact with his family after a feud over inheritance, they told Reuters, and moved to Saudi Arabia when his daughter was a toddler. There, it seems, he turned to a stricter form of Islam.

"From what we heard, they lived differently, their mindset is different. We are from a land of Sufi saints... this is very shocking for us," said school teacher Hifza Bibi, the step-sister of Malik's father, who lives in Karor Lal Esan town in central Punjab province.

Sufism emphasises a mystical, personal religious connection.

"Our brother... went to Saudi and since then he doesn't care about anyone here," Bibi said. "A man who didn't come to attend his own mother's funeral, what can you expect from him?"

Also read: California couple’s home thrown open to media

Tashfeen Malik returned to Pakistan and studied pharmacy at Bahauddin Zakaria university in Multan from 2007 to 2012. She lived in a university hostel. An identity card said she was 29 years old at the time of the shootings.

"She was known to be good student with no religious extremist tendencies," an intelligence official based in the nearby town of Layyah told Reuters.

Malik's uncle Javed Rabbani, a clerk in the town's education department, said he has not seen his brother in 30 years.

"We feel a lot of sadness but we also feel ashamed that someone from our family has done this," he said.

"We can't even imagine doing something like this. This is a mindset that is alien to us."

Malik visited Pakistan in 2013 and 2014, security officials told Reuters, but it's unclear who she met or where she visited.

On Saturday, the militant Islamic State (IS) group claimed the couple as their followers in a broadcast. However, there is no evidence yet that IS directed the attack or even knew the attackers.

IS also claimed responsibility for a Nov 13 series of attacks in Paris in which gunmen and suicide bombers killed 130 people.

The broadcast came a day after Facebook confirmed that comments praising IS were posted around the time of the shooting to an account set up by Malik under an alias.

The pair, who had left their six-month-old baby daughter with relatives, were killed in a shootout with police SWAT team members.

Also read: California couple’s home thrown open to media

Federal agents tore through a garage door to search a house in Riverside, a few km southwest of San Bernardino, on a street where neighbours said Farook once lived.

An FBI spokeswoman confirmed agents made a "precautionary tactical entry" while serving a federal search warrant, but she declined to give details.

Neighbours named the man who lived there as Enrique Marquez and said he was often seen with Farook.

NBC News said the house belongs to a man who authorities believe bought the rifles used in the attack.

As investigators probe Wednesday's rampage as an act of terrorism, the White House said President Barack Obama will address the nation on Sunday evening to update the public.

If the Dec 2 mass shooting proves to have been the work of people inspired by Islamist militants, it would be the deadliest such attack in the United States since Sept 11, 2001.

Obama to make primetime address

US President Barack Obama will make a rare primetime address to the nation Sunday laying out how he will keep Americans safe and defeat the IS group.

Obama declared in his weekly address on Saturday that the United States “will not be terrorised... We are Americans. We will uphold our values — a free and open society.“

'Whole new approach'

Jeh Johnson, the secretary of Homeland Security, told the New York Times the country has entered "an entirely new phase" in the global threat from extremists.

Enemies such as IS have "in effect outsourced attempts to attack our homeland", he told the newspaper. "We've seen this not just here but in other places. This requires a whole new approach, in my view."

FBI officials say Farook and Malik seem to have been inspired by foreign militant groups, but that there was no sign they worked with any of them or that IS even knew who they were.

While Obama's team has not yet found evidence the couple was part of an organised group or broader terrorist cell, it said on Saturday that "several pieces" of information "point to the perpetrators being radicalised to violence."

If that turned out to be the case, Obama said in a radio address, it would underscore a long-recognised threat: "the danger of people succumbing to violent extremist ideologies".