Wang Youcai (l) was welcomed by fellow dissident Xu Wenli

Mr Wang, one of the founders of the outlawed China Democracy Party, was sentenced to 11 years in jail in 1998.

He is staying with fellow dissident Xu Wenli who was released from a Chinese prison in December 2002.

He was freed on Thursday in a move hailed by the United States, but seen by some as an attempt by China to ameliorate its human rights record.

The development comes ahead of an annual UN human rights meeting in Geneva at which the US was considering criticising China's rights record.

"I'm not sure what exactly is going on," Mr Wang said on his arrival at TF Green Airport in Warwick, Rhode Island, on Thursday night. "I need time to clear my head."

CHINA DEMOCRACY PARTY Set up by dissidents in 1998 First attempt to legally register an opposition party Quickly crushed by Communist Party At least 30 members sentenced to jail terms of up to 13 years Co-founders Xu Wenli released 2002, Qin Yongmin still imprisoned

US State Department spokesman Richard Boucher said on Thursday that the dissident had been "imprisoned for attempting to exercise basic freedoms of speech and assembly and China".

"We once again call on Chinese government to release all prisoners detained for peaceful expression of their views," Mr Boucher added.

Mr Wang was welcomed on his arrival on Rhode Island by Xu Wenli, who like Mr Wang was imprisoned for his part in the 1989 Tiananmen Square protests, and his part in co-founding the China Democracy Party.

Mr Xu said Mr Wang's release was merely a gesture by the Chinese government.

"It doesn't mean Chinese human rights have improved, he said. "We were arrested and also used as a bargaining chip."

Medical worries

Mr Wang, 37, first came to prominence as one of the student leaders involved in the 1989 Tiananmen Square demonstrations, which were brutally suppressed by the Chinese authorities at the cost of several hundred lives.

Mr Wang, a physics graduate from Peking University, was described by the authorities as one of the "most wanted" students, and was jailed for taking part in the protests.

In 1998 he was sentenced again, for his part in founding the China Democracy Party, the first attempt to set up a legal opposition to China's ruling Communist Party.

Communist officials outlawed the party soon after its inception, jailing more than 30 people for taking part.

Mr Wang was tried on the charge of "subverting state power", and was accused of organising meetings, using computer e-mail to send information and accepting donations from overseas.

Timely decision

His release, more than five years ahead of schedule, came on the eve of the Chinese parliament's National People's Congress, which is expected to enshrine a commitment to human rights in China's constitution.

The US-based rights group the Dui Hua Foundation said Mr Wang had suffered from bronchial disorders and was recently diagnosed with myocarditis, an inflammation or degeneration of the heart's muscle tissue.

But it is difficult to determine how far his medical conditions played a part in his release.

A BBC correspondent in Beijing, Louisa Lim, says that medical parole for treatment overseas is often used as a way to send unwanted individuals into exile.

The release came one day after Chinese authorities cut the sentence of another prominent prisoner - the Uighur businesswoman Rabiya Kadeer.

She was sentenced to eight years in jail in 2000 on charges of separatism, but is now due to be released in August 2006, or even sooner, according to the Dui Hua Foundation.