By Dustin Volz

WASHINGTON (Reuters) - Chelsea Manning, the U.S. soldier imprisoned for leaking classified files to pro-transparency site WikiLeaks, attempted to commit suicide last week, her lawyers said on Monday.

“Last week, Chelsea made a decision to end her life,” attorneys Chase Strangio, Vincent Ward and Nancy Hollander said in a joint statement. “Her attempt to take her own life was unsuccessful.

The statement confirms earlier media reports that said Manning's hospitalization last week near the U.S. Disciplinary Barracks at Fort Leavenworth, Kansas, resulted from a suicide attempt.

The lawyers said Manning, 28, is under close supervision and expects to remain on that status for several weeks.

They said the U.S. military committed a “gross breach of confidentiality” for revealing her “personal health information” and hospitalization to the press.

The Pentagon did not immediately respond to a request for comment. The U.S. Army had not officially confirmed the hospitalization was due to a suicide attempt.

Manning, a former intelligence analyst in Iraq, is serving a 35-year sentence after a 2013 military court conviction of providing more than 700,000 documents, videos, diplomatic cables and battlefield accounts to WikiLeaks. It was the biggest breach of classified materials in U.S. history.

Among the files that Manning turned over to WikiLeaks in 2010 was a gunsight video of a U.S. Apache helicopter firing at suspected Iraqi insurgents in 2007. A dozen people were killed, including two Reuters news staff.

Manning, who was born male but identifies as a woman, in May appealed to a military court to overturn her court-martial conviction.

Her lawyers have said she was held in unlawful pretrial detention for nearly a year and that her punishment is excessive, a claim civil liberties and government transparency advocates have echoed.

(Editing by Jeffrey Hodgson)