The FBI reportedly paid more than $1.3m (£900,000) to a secret group to crack into the San Bernardino shooter's iPhone but agency director James Comey said it was "worth it".

Comey said the money was well spent even though FBI officials conceded they are yet to access any significant information on the phone. Officials had hope to track other terror cells linked to the owner of the iPhone 5C, Syed Farook, who killed 14 people at a 2015 office holiday party in San Bernardino, California, along with his wife Tashfeen Malik.

The agency director indicated the hefty price tag while speaking at the Aspen Security Forum in London, the Wall Street Journal reported. When he was asked by a moderator how much the FBI paid to an undisclosed outside group to demonstrate how to hack into the iPhone, Comey at first said: "A lot."

Then he added: "Let's see, more than I will make in the remainder of this job, which is seven years and four months, for sure." Using math based on his salary over that period, the cost had to be at least $1.3m, the New York Times calculated. The FBI wouldn't confirm the price tag but the cost is in line with such an operation, according to the Times.

Comey did not, however, offer any hints as to the identity of the group the FBI used to help hack into the phone. Some media reports have named an Israeli security firm but there has been no confirmation yet.

The agency had wrangled for weeks with Apple inside and outside of a courtroom in a failed bid to get the tech company to break into one of its own phones. The FBI finally turned for help to another group.

The Justice Department is still trying to force Apple in court to help unlock encrypted phones in Brooklyn, Boston and elsewhere.