Chelsea Manning, the transgender US soldier serving a 35-year sentence for a notorious intelligence leak, said Tuesday she is temporarily barred from recreational activities for possessing contraband items and for "disorderly conduct."

Manning, whose birth name is Bradley, had faced solitary confinement for the four offenses that were weighed by a disciplinary board at Fort Leavenworth prison in Kansas.

Manning said on Twitter she could not use the gym, library or go outdoors for three weeks after the board found her guilty.

Additionally, the punishment means Manning could spend more time in the high-security prison, as it represents a strike against her good-behavior record.

"These convictions will follow me thru to any parole/clemency hearing forever," she wrote on Twitter.

"Was expecting to be in (minimum) custody in Feb, now years added."

She tweets from prison by dictating messages on the phone to supporters.

According to charge sheets published by supporters, Manning showed "disrespect" during a July 2 meal and was "observed sweeping food onto the floor."

She was also found to have been in possession of contraband books, magazines and expired toothpaste.

The website chelseamanning.org said Manning, who underwent hormone treatment to become a woman, was in possession of the Vanity Fair magazine featuring Caitlyn Jenner, the former US Olympian who underwent a sex change.

Chase Strangio, one of Manning's attorneys, released a statement decrying the punishment.

"She also will carry these infractions through her parole and clemency process and will be held longer in the more restrictive security facility where she is now incarcerated," said Strangio, of the American Civil Liberties Union rights group.

"No one should have to face the lingering threat of solitary confinement for reading and writing about the conditions we encounter in the world."

The former army intelligence analyst was convicted in August 2013 of espionage and other offenses after admitting to handing more than 700,000 classified documents, including military intelligence reports and State Department cables, to the anti-secrecy website WikiLeaks.

US officials describe Manning's document dump as the biggest leak of classified files in American history.

Manning has become something of a dual symbol, embodying the fight against government secrecy and the plight of transgender Americans.

More than 100,000 people signed a petition, delivered to the military on Tuesday, calling on the government not to sentence Manning to solitary confinement.