By David Ingram

NEW YORK (Reuters) - U.S. Army soldier Chelsea Manning, who is serving 35 years in prison for passing classified files to WikiLeaks, was sentenced to 14 days in solitary confinement as punishment for attempting suicide and keeping a banned book in her cell, supporters said on Friday.

A disciplinary board at the Fort Leavenworth, Kansas, military prison where Manning is incarcerated informed her of the decision after a hearing on Thursday, according to a statement by Fight for the Future, a group supporting her.

No date was given for the sentence to start. Manning was quoted in the statement saying she could appeal the punishment and that seven days of it would be suspended provided she stayed out of trouble for six months.

"I am feeling hurt. I am feeling lonely. I am embarrassed by the decision. I don't know how to explain it," Manning said.

Army spokesman Wayne Hall said in an email: "It would be inappropriate for the Army to comment at this time."

Manning, 28, is a transgender Army private who was born male and revealed after being convicted of espionage that she identifies as a woman. She tried to take her own life in July after what her lawyers said was the Army's denial of appropriate healthcare.

This month, Manning went on a hunger strike, agreeing to end it only when the Army said she would be allowed to receive gender transition surgery. She began hormone therapy in 2015.

A lawyer for Manning, Chase Strangio of the American Civil Liberties Union, questioned the logic of "our systems of incarceration punishing people with the cruelty of solitary for attempting to end their life."

Manning has been a focus of a worldwide debate on government secrecy since she provided more than 700,000 documents, videos, diplomatic cables and battlefield accounts to the anti-secrecy group WikiLeaks.

The case ranked as the biggest breach of classified materials in U.S. history. Manning, a former intelligence analyst in Iraq, in 2013 drew a 35-year prison sentence.

Military parole rules could allow her to leave prison after serving seven years.

Among the files Manning leaked in 2010 was a gunsight video of a U.S. Apache helicopter firing on suspected Iraqi insurgents in 2007, an attack that killed a dozen people, including two Reuters news staffers.

Manning said the prohibited book in her prison cell was "Hacker, Hoaxer, Whistleblower, Spy" by Gabriella Coleman, about the computer hacker group Anonymous.

(Reporting by David Ingram; Editing by Jonathan Oatis and Dan Grebler)