NSA collects under 30% of all phone data: Reports

Lawmakers have suggested the NSA's controversial bulk phone data programme scooped up virtually every phone call in America, but officials told the Washington Post and the Wall Street Journal the agency has struggled to gather data from mobile phones.

The explosion in cellphone use has presented a technical and logistical problem for the eavesdropping agency, which has a much more comprehensive collection of landline phone records, the newspapers said.

The controversial program, first revealed during George W Bush's presidency, seeks to track extremists or other intelligence targets by scooping up phone records, including the numbers called and the duration of the calls, but not the content of the conversations.

The bulk data collection once covered close to 100 percent of Americans' phone records, but last year the portion dropped to between 20 to 30 percent, current and former officials told the newspapers.

The NSA is moving to close the gap and will seek court orders to force telecommunications companies to hand over phone records, if they are not already doing so, officials told the papers.

When collecting phone data, the spy service has to take steps to avoid obtaining mobile phone tower details that are not allowed under the program, it said.

The current bulk data program does not cover at least two wireless firms -- Verizon Wireless and T-Mobile, according to the Wall Street Journal. And it was unclear if it included Internet-based calls.

In a request for comment on the reports, the NSA told AFP it would not "discuss specific intelligence collection methods," saying that it is "always evaluating our activities to ensure they are keeping pace with changes in technology."

But the reports suggested the program was less extensive and less effective than widely believed.

The relatively low percentage still may translate into tens of billions of phone records going back five years, which civil liberties groups say signifies a major breach of privacy rights.

But Deputy Attorney General James Cole told lawmakers in July that collecting a large amount of records is necessary to pinpoint terror suspects.

"If you're looking for the needle in the haystack, you have to have the entire haystack to look through," Cole said.

The account comes amid a growing "big brother" image of the NSA in the wake of revelations from intelligence leaker Edward Snowden, the former IT contractor who lifted the lid on the agency's vast electronic spying activities.

Amid global outrage sparked by the Snowden media leaks, President Barack Obama last month proposed that the phone data be taken out of the government's hands and shifted elsewhere to allay privacy worries.

The Justice Department and the country's intelligence agencies have until March 28 to come up with a plan on the data storage.