BEIJING, May 7 (Reuter) - A Chinese court sentenced three Tibetans, including two former officials, to jail terms of up to six years for separatism and leaking state secrets after a trial behind closed doors, the Xinhua news agency said on Wednesday.

The Intermediate People's Court of Xigaze prefecture sentenced Qazha Qamba Chilai, 58, former vice-chairman of the Tibet Autonomous Regional Committee of the Chinese People's Political Consultative Conference, to six years in prison.

The conference is an advisory group to parliament.

He was convicted of trying to split the country and leaking state secrets, Xinhua said.

A second official Qamba Qung and Samzhub, a businessman, were sentenced to four and two years in prison respectively, the agency said, adding that all three defendants confessed.

The sentences were handed down on April 21, it said without giving a reason for the delay in reporting them.

The sentences went into effect on May 5 after the three defendants "indicated acceptance of the rulings and would not appeal," it said.

The defendants "colluded with separatist forces abroad," Xinhua quoted the verdict as saying.

"They have seriously jeopardised the national unification and unity of ethnic groups, damaged the stability and development of Tibet and have committed the crime of splitting the country," it said.

The court "diminished the penalties of the three accused on the charge of conspiring to split the country," Xinhua said. It did not elaborate.

China has come under fire from rights groups and Western governments for its heavy-handed treatment of those seeking independence for Tibet.

In March, the European Parliament accused China of persistent human rights violations in Tibet and urged Beijing to end its refusal to negotiate the Himalayan region's future with its exiled spiritual leader, the Dalai Lama.

Beijing dismisses criticisms as interference in its internal affairs and has slammed the West for using Tibet as a tool to split China.

Chinese troops marched into Tibet in 1951 and suppressed a rebellion in the remote and mountainous region in 1959 that forced the Dalai Lama and thousands of followers to flee into exile in India.

The Dalai Lama won the Nobel Peace Prize in 1989 for his non-violent campaign for more autonomy for his homeland.

Tibet has been rocked in recent years by sporadic, sometimes violent, anti-Chinese unrest, with monks and nuns often at the forefront of demonstrations for independence.

Authorities tightened security and launched a manhunt across the deeply religious region, which borders India, Nepal, Bhutan and Burma, after a bomb exploded on Christmas Day outside government offices in Tibet's capital, Lhasa.