WASHINGTON - The Army has detained a 22-year-old soldier in Baghdad in connection with the leak of a military video that shows Apache helicopters gunning down unarmed men in Iraq, including two journalists, defense officials said Monday.

Army Spc. Bradley Manning of Potomac, Md., who is being held in Kuwait pending the results of an investigation, is the third suspected leaker known to have been apprehended under the Obama administration.

"This is a startling pattern for anyone who's been watching the field for a while," said Steven Aftergood, a director of the Project on Government Secrecy at the Federation of American Scientists.

"It certainly shows that this administration is aggressively pursuing leakers," he said, and that "there is essentially zero tolerance for public disclosure of classified information."

A convicted computer hacker from California alleged that he alerted authorities about Manning after meeting him online, calling the young military analyst "a good kid who got a little mixed up."

Lt. Col. Eric Bloom, an Army spokesman, said Monday that Manning had not yet been charged with a crime. He said it wasn't possible to predict how long Manning would be held in confinement without being charged.

Pentagon spokesman Bryan Whitman said Manning's involvement in the 2007 video provided to WikiLeaks.org was "something [U.S. authorities] were looking at."

State Department spokesman P.J. Crowley said the department was helping the Army investigate because the case includes classified State Department reports.

The classified video was taken from the cockpit during a 2007 firefight and posted in April on WikiLeaks. It was an unflattering portrait of the war that raised questions about the military's rules of engagement and whether more should be done to prevent civilian casualties.

The video shows a group of men walking down the street before being repeatedly shot by the helicopters. The American gunners can be heard laughing and referring to the men as "dead bastards." Among those believed to have been killed in that attack were Reuters photographer Namir Noor-Eldeen, 22, and his driver, Saeed Chmagh, 40. Two children were wounded.

An internal investigation concluded that the troops had acted appropriately. According to a July 19 summary of the results of the inquiry, Reuters employees were likely "intermixed among the insurgents" and difficult to distinguish, the document states.

Former hacker Adrian Lamo said he alerted the military after Manning confided in him online that he had leaked the video in addition to 260,000 classified diplomatic cables. In 2004, Lamo pleaded guilty to breaking into the New York Times' computer system and still owes $62,800 in federal restitution. He said he had received no financial benefit from turning in Manning.