BEIJING (REUTERS) - Disgraced former senior Chinese leader Bo Xilai is refusing to cooperate with a government investigation into him and has staged hunger strikes in protest and at one point was treated in hospital, sources with knowledge of the matter said.

Almost a year after Bo's fall from grace under a cloud of lurid accusations about corruption, abuse of power and murder, the government has given no definitive time frame for when he will face court, and has not even announced formal charges.

Bo was ousted from his post as Communist Party chief in the southwestern city of Chongqing last year following his wife's murder of a British businessman, Neil Heywood.

Before that, Bo, 63, had been widely tipped to be promoted to the party's elite inner core. His downfall came after his estranged police chief, Wang Lijun, fled briefly to a U.S. consulate last February and accused Bo's wife, Gu Kailai, of poisoning Mr Heywood. Gu and Wang have both since been convicted and jailed.

No criminal charges against Bo have been revealed but the ruling Communist party has accused him in statements carried by the official Xinhua news agency of corruption and of bending the law to hush up Heywood's killing.

Two independent sources with ties to the family said Bo's trial was likely to be delayed until after an annual full session of parliament and its top advisory body in March because he was not physically fit. "He was on hunger strike twice and force fed," one source told Reuters, requesting anonymity due to the sensitivity of the case. It was unclear how long the hunger strike lasted.

"He was not tortured, but fell ill and was taken to a hospital in Beijing for treatment," the source said, declining to provide details of Bo's condition and whereabouts which have been kept under wraps since his downfall.

The stability-obsessed ruling party is determined to prevent anything, including Bo's trial, from disrupting the final steps of Vice President Xi Jinping's ascent to becoming top leader.

Mr Xi, who assumed leadership of the party and military in November, will take over from Hu Jintao as state president during the annual session of parliament, beginning on March 5.

Aware of public anger about a succession of officials caught up in graft cases, Xi has made fighting graft one of his main themes, saying that nobody, no matter how senior, is above the law. He has said that the party's survival is at stake if the issue is not tackled.