Tashfeen Malik and husband Syed Farook visited ranges in the Los Angeles area, said David Bowdich, assistant director of the FBI's Los Angeles office,  BBC reported.

He said both were radicalised and had been "for some time".

The US is investigating last week's attack, which happened at a health care centre, as an act of terrorism.

But Mr Bowdich said there is no evidence yet that last week's tragedy, the most deadly terror attack in the US since 9/11, was plotted from overseas.