San Bernardino shooting: Tashfeen Malik may have radicalised American-born husband Syed Farook, US officials say

Authorities investigate whether the wife was the 'main driving force' behind the couple's attack on a centre for the disabled in California

Tashfeen Malik, left, and Syed Farook died in a shoot-out with police (AP)

US investigators say San Bernardino shooter Tashfeen Malik may have radicalised her American-born husband.

Police in California are investigating whether Malik, who was born in Pakistan, was the "driving force" behind the massacre plot after it emerged she had pledged allegiance to Isis in a Facebook post.

Malik and her husband, Syed Farook, opened fire on a centre for disabled people with assault-style rifles on 2 December - killing 14 people.

The couple were killed a hours later in a shootout with police - leaving behind a six-month-old daughter.

An unnamed US official said they were trying to establish whether Malik had contact with Islamist militants in Pakistan and Saudi Arabia.

Malik's estranged relatives in Pakistan have said she appeared to have abandoned the family's moderate Islam and become more radicalised in Saudi Arabia, where she moved as a toddler.

She returned to Pakistan and studied pharmacy at Bahauddin Zakaria University in Multan from 2007 to 2012.

Farook and Malik are believed to have met through a Muslim dating website.

Malik came to the US on a fiancee visa two years ago.

Authorities are increasingly convinced the pair were planning multiple attacks after a stockpile of weapons was found in their home.

US Attorney General Loretta Lynch said authorities have no evidence that the shooters were part of a larger terrorism cell but were working with their counterparts overseas to gather information about their lives.

Ms Lynch told NBC: "We are trying to learn everything we can about both of these individuals.

"It will be a long process, it will be an exhaustive process."

Additional reporting by Reuters