BAGHDAD  An American soldier in Iraq who was arrested on charges of leaking a video of a deadly American helicopter attack here in 2007 has also been charged with downloading more than 150,000 highly classified diplomatic cables that could, if made public, reveal the inner workings of American embassies around the world, the military here announced Tuesday.

The full contents of the cables remain unclear, but according to formal charges filed Monday, it appeared that a disgruntled soldier working at a remote base east of Baghdad had gathered some of the most guarded, if not always scandalous, secrets of American diplomacy. He disclosed at least 50 of the cables “to a person not entitled to receive them,” according to the charges.

With the charges, a case that stemmed from the furor over a graphic and fiercely contested video of an attack from an American helicopter that killed 12 people, including a reporter and a driver for Reuters, mushroomed into a far more extensive and potentially embarrassing leak.

The charges cited only one cable by name, “Reykjavik 13,” which appeared to be one made public by WikiLeaks.org, a whistle-blowing Web site devoted to disclosing the secrets of governments and corporations. The Web site decoded and in April made public an edited version of the helicopter attack in a film it called “Collateral Murder.”