WASHINGTON: Three US news media groups filed a lawsuit Friday to get the FBI to release details of how it hacked the iPhone of the man who with his wife shot and killed 14 people in San Bernardino last year.

The Federal Bureau of Investigation said it wanted to access Syed Rizwan Farook's locked iPhone 5c to look into possible links to the Islamic State group, but phonemaker Apple refused to help, citing privacy concerns.

Gannett — USA Today's parent company — the Associated Press and Vice Media are suing to obtain details of the mysterious hack that rekindled a national debate on communications encryption and privacy protection.

Syed Rizwan Farook and his wife Tashfeen Malik killed 14 people at a holiday gathering in San Bernardino, California, in December. They were also killed by police after a chase.

The federal law enforcement agency took Apple to court in February to compel them to help, but dropped the suit weeks later after hacking the phone with third-party help.

The FBI has yet to name the outside party or the cost involved.

“Understanding the amount that the FBI deemed appropriate to spend on the tool, as well as the identity and reputation of the vendor it did business with, is essential for the public to provide effective oversight of government,” reads the lawsuit, filed in the US capital Washington.

Apple Inc., which makes computers and iPhones, had said that it would not obey an order from a US federal judge to help the FBI access data on a phone used by San Bernardino shooters.

In an open letter to Apple customers, the company’s CEO, Tim Cook, said he could not accept this “unprecedented step”, which “threatens the security” of its customers. We oppose this order, which has implications far beyond the legal case at hand,” he wrote.

“This moment calls for public discussion, and we want our customers and people around the country to understand what is at stake.”

Cook noted that smartphones had become an essential part of people’s lives who use them to store “an incredible amount of personal information”, from private conversations to photos, music, notes, calendars, contacts, financial information and health data, “even where we have been and where we are going”.