Republican Senator Pat Roberts who heads the Senate Intelligence Committee, said he would not allow the committee "to be politicized or to be used as an unwitting tool for any political strategies."

"About the question of an official, joint investigation: it's very premature," Roberts told a joint press conference with Representative Porter Goss of Florida, and Senator John Warner, chairman of the Senate Armed Services Committee.

Roberts said criticism of the work of US intelligence services would create "divisiveness" with the intelligence committee and the US Department of Defense.

And before any official inquiry was launched, the various committees in charge of supervising intelligence gathering activities would investigate and interview witnesses, he said.

"When the committee deems it appropriate we will make whatever public statements that are necessary," he said.

The Senate Armed Services Committee's top Democrat Carl Levin, and top Democrat on the Intelligence Committee John Rockefeller have called for a more official investigation, jointly by the committees of both houses and followed up by the publication of a report.

"You need a structure for an inquiry: what is it we're looking for?" Levin said.

He said the hearings' proceedings should be made public as soon as possible.

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