Biden told NBC television that Washington wanted to help Chen take up the offer of a fellowship from New York University.

"We're prepared to give a visa right away. He's going to be able to take his family. We expect the Chinese to stick to that commitment," Biden said.

Chen is at the center of a major diplomatic wrangle between China and the United States after he escaped harsh house arrest in the eastern province of Shandong late last month and sought refuge at the US embassy in Beijing.

He has been offered the fellowship but injuries sustained during his flight and official restrictions on access to him have prevented him from completing the necessary formalities to leave.

Chen on Sunday appealed for official help to leave China, saying he was effectively blocked in his hospital bed in Beijing.

"Now I have notified the hospital to invite them (government officials) to help me do the procedures. I really don't have a way," he told AFP in a telephone interview.

"It's even difficult for me to get out of bed and my other friends cannot come, so I have no way. They (US diplomats) have come, but they can't see me."

Senator John McCain, who was the Republican 2008 presidential nominee, said there had been "a number of missteps" in the handling of Chen's case.

But he told ABC television "the key now right now is to get him out of there and to the United States. That's I think what we all ought to focus on.

"It's important to recognize that people who helped him are being rounded up and detained. People are being arrested," McCain added.

"We've got to focus a lot of attention on them, as well. But first priority is to get him out of there and to the United States."

The delicate diplomatic standoff over Chen's move to seek sanctuary in the US embassy in Beijing and his later request to leave China, became fodder on the presidential campaign trail.

The president's presumed White House rival, Mitt Romney suggested in a sharp critique last week that the administration had mishandled the Chen affair by allowing the dissident to leave the embassy before it was completely clear that he and his family faced no threat of retaliation and truly wanted to stay in China.

"This is a dark day for freedom and it's a day of shame for the Obama administration. We are a place of freedom, here and around the world, and we should stand up and defend freedom wherever it is under attack," Romney said last week.

But speaking on ABC television Sunday, President Barack Obama's campaign strategist David Axelrod dismissed the criticism, saying "we want to help Mr Chen achieve his goal, which is to come here, and we want to do it in accordance with our values, and we want to be successful in doing that. And we're making some progress in that regard," Axelrod said.

He also leveled a swipe at Romney.

"What's shameful is when presidential candidates are so craven to score political points that they speak irresponsibly on half-information at a time when the president is trying, and the administration is trying, to resolve a situation that is very, very sensitive and very difficult," he said.

Chen is at the centre of a major diplomatic wrangle between China and the United States after he dramatically escaped harsh house arrest in the eastern province of Shandong and sought refuge at the US embassy in Beijing.

He has been offered a fellowship from New York University but injuries sustained during his flight and official restrictions on access to him have prevented him from completing the necessary formalities to leave.

The activist was escorted to the Beijing hospital by US officials on Wednesday, but said his friends had been barred from visiting and US diplomats had only been allowed to see his wife, who was with him at the facility.

"Now I have notified the hospital to invite them (government officials) to help me do the procedures. I really don't have a way," he told AFP in a telephone interview.

"It's even difficult for me to get out of bed and my other friends cannot come, so I have no way. They (US diplomats) have come, but they can't see me."

Chen, who riled authorities by exposing forced abortions and sterilisations under China's "one-child" policy, says he wants to depart for the United States for his safety and that of his wife and two young children.

China's foreign ministry said on Friday that he would be allowed to apply to study abroad, signalling then-visiting US Secretary of State Hillary Clinton had secured a deal with the Chinese government.

Chen, 40, a self-taught lawyer, is in hospital being treated for foot injuries sustained during his escape from his village home, where he says he was beaten and kept under constant surveillance.

Friends of the dissident told AFP Chen and his family were preparing to go to the United States and might leave soon though his departure would depend on the Chinese government giving permission and issuing passports.

Jerome Cohen, a New York University professor who is a friend and adviser to Chen, said he may go to the United States "soon".

"I'm hoping it's a done deal. I was very excited when I saw the announcement by the foreign ministry spokesman on Friday afternoon," Cohen told AFP by telephone from his US home.

"That's an open signal that they are prepared to let him come abroad for a period of study," said Cohen, who spoke to Chen twice before he left the US embassy but not since.

A spokesman for New York University said Friday that the activist had been invited to study there.

Chen said he did not know how long he would be in hospital, but fellow activist lawyer Jiang Tianyong, who spoke to him by phone late Saturday, said he would probably be in the hospital a few more days for treatment.

"The current situation is that he hopes he and his family can go together to the United States," Jiang told AFP on Sunday. "He hopes to come back."

The entrances of the Chaoyang Hospital compound remained tightly guarded by uniformed police on Sunday and the wary authorities kept journalists in a designated area outside, an AFP photographer at the scene said.

If Chen decides to take up the NYU offer, he would be a visiting scholar at the law school with a programme of study and lecture, Cohen said.

"I wouldn't be surprised if he got here within a week. But if it takes a month, it doesn't matter and it wouldn't surprise me either," he said.

US officials appeared to be keeping the details, including a timescale, of any agreement with Beijing deliberately vague, fearing that it would fall through if China felt embarrassed on its home soil.