Leon Panetta, the US defence secretary, has ordered senior Pentagon officials to begin monitoring major US news media for disclosures of classified information in an effort to stop the release of government secrets in the wake of a series of high-profile leaks.
The announcement on Thursday came hours after Panetta and other senior defence officials appeared before a closed-door hearing of the House of Representatives Armed Services Committee to discuss recent disclosures of classified security information.
Reports about US cyber warfare against Iran, procedures for targeting fighters with drones and a double agent who penetrated an armed group in Yemen have angered US lawmakers. Some have charged the leaks were timed to benefit President Barack Obama's re-election bid.
Representative Buck McKeon, the Republican chairman of the House panel, told a news conference later that he did not
believe the Pentagon was behind the leaks and that Panetta and the other officials were taking the issue seriously.
Panetta, Army General Martin Dempsey, the top uniformed military officer, and chief Pentagon lawyer Jeh Johnson appeared before the committee to answer questions. McKeon said they agreed the recent leaks had caused damage, but did not elaborate.
In addition to the media monitoring ordered by Panetta, the Pentagon said it had taken a number of other steps in recent months to improve information security.
Publication of manual
The measures included improved training for handling classified information, the publication of a manual with clear instructions on what constitutes an unauthorised disclosure and the creation of an online security incident reporting system.
"The department is continuously improving its security posture and overall capability to prevent unauthorised disclosures," the Pentagon said in a statement disclosing the recent security changes.
McKeon said the House panel was "concerned about the leaks that have come out over the years and accelerated, it seems, over the last few months".
Although he said he did not believe the Pentagon was the source of the most recent leaks, McKeon declined to comment on speculation the White House was responsible.
Senator John McCain, Obama's Republican opponent in the 2008 presidential election, has suggested some of the leaks may have been calculated to boost the Democratic president's re-election efforts - a charge the White House emphatically denies.
George Little, the Pentagon Press Secretary, told a briefing on Thursday that Panetta, Dempsey and members of the House committee were of one mind about the leaks.
"The unauthorised disclosure of classified information is truly disturbing," he said. "It's of concern to the secretary, and I think members on the Hill express similar concern. And the secretary is clearly prepared to try to address the problem inside the department."