Supporters of WikiLeaks soldier heckle Obama

President Barack Obama speaks at a fundraiser at Nob Hill Masonic Center in San Francisco, April 20, 2011.

SAN FRANCISCO (Reuters) - Protesters interrupted President Barack Obama at a campaign fund-raiser on Thursday to complain about the treatment in detention of a U.S. soldier accused of leaking documents that appeared on the WikiLeaks website.

Obama's administration has been criticized for Bradley Manning's treatment, although the president says the Pentagon has assured him the soldier is not being ill-treated while he is awaiting trial.

Obama was addressing a room of about 200 people -- many of whom paid as much as $35,800 to see him -- when a woman in a white suit stood up and announced that she and nine others sitting at her table had written a song for him.

Despite Obama's protestations, they then broke into a song that called for the 23-year-old soldier's release. They passed out "Free Bradley Manning" signs and the woman took off her jacket to reveal a black T-shirt with Manning's image.

"Now, where was I?" the somewhat flustered president said after the group stopped. "There's an example of creativity."

Manning is being held during an investigation of charges involving reams of sensitive diplomatic and military documents he is accused of leaking while posted as an intelligence analyst in Iraq. Many of the documents appeared on the WikiLeaks website.

U.S. military officials have not said when Manning's trial might begin, but he was transferred on Wednesday to a detention facility at Fort Leavenworth military base in Kansas after his lawyers complained he was being mistreated at a Marine brig in Virginia.

He was kept alone in his cell 23 hours per day and forced to sleep naked while being awakened repeatedly during the night. The Pentagon said this was done to ensure his well-being and that it had only happened on a few occasions.

(Reporting by Jeff Mason; Editing by Vicki Allen)