The top US lawmakers on intelligence issues stood united Thursday in demanding an end to a "cascade" of national security leaks they warn put lives at risk, but stopped short of saying the breaches were politically motivated.

Senate intelligence committee chair Dianne Feinstein said she wants Congress to swiftly enact legislation tightening rules on data sharing and breaches, and welcomed an investigation launched by the FBI into leaks that have infuriated lawmakers on both sides of the aisle.

But she held back on calling for a special prosecutor to look into the leaks, which some Republicans, notably Senator John McCain, say were done in order to make President Barack Obama look tough against Iran and terror networks in a US election year.

"A special prosecutor can take years," Feinstein told reporters, with committee ranking Republican Saxby Chambliss and the two leaders of the House intelligence committee at her side.

"We don't have years. We need to legislate, we need to get some solutions before us very quickly."

The bipartisan quartet was briefed Thursday by the Director of National Intelligence, James Clapper, who Chambliss said was "extremely upset" about the leaks.

The group said they were also due to meet later Thursday with FBI chief Robert Mueller, whose agency has launched an official investigation.

"All of us are extremely upset about the fact that not only have leaks occurred but there's been just a cascade of leaks coming out of the intelligence community over the last several weeks and months," Chambliss said.

Three explosive stories have emerged in recent weeks: Obama's push for cyber attacks on computers that run Iran's nuclear facilities; an apparent "kill list" of counterterrorism targets against whom Obama has authorized lethal action; and a secret drone campaign against terrorists in Yemen.

The New York Times reported that sources for their articles on the covert programs were former or current administration officials.

Republican House intelligence committee chairman Mike Rogers said it was too early to determine whether the leaks had a political bent.

But "to have all four of us come forward today and talk about the severity of these leaks I hope sends a very clear message about how dangerous this has become," Rogers said. "There is a clear need for a formal investigation."

Feinstein sought to downplay the potential fallout of a major investigation during an election year, saying a probe should not be seen as a political ploy against the president.

"This is not fingerpointing at anybody," she said. But "this has to stop."

Chambliss agreed. "This is not meant to be a political exercise," he said "This is too critical to the future of the intelligence community."