An Apple logo hangs above the entrance to the Apple store on 5th Avenue in the Manhattan borough of New York City in this file photo taken July 21, 2015. [Photo/Agencies]

SAN FRANCISCO - A federal judge ordered tech company Apple on Tuesday to help the Federal Bureau of Investigation (FBI) access the phone of a terrorist killer.

The ruling by Judge Sheri Pym of the US District Court, Central California, was in response to federal prosecutors investigating the attack by Syed Farook and his wife Tashfeen Malik on Dec 2 last year in San Bernardino, California.

The two shot dead 14 people at a holiday luncheon before both were killed by police.

Investigators told Pym that without a password, they were unable to look into an iPhone used by Farook.

It has been increasingly a standard procedure for US law enforcement to look into suspects' electronic devices including personal computers and smartphones and social network postings, especially in terror-related cases.

The smartphone used by Farook was a work phone owned by San Bernardino County, where the suspect worked at the public health department.

Pym ordered Apple, the maker of iPhone, to provide specialized software designed to bypass a security feature that erases data in the device after a certain number of unsuccessful unlocking attempts, so that the FBI would be able to hack into the phone.