In a wide-ranging interview on NBC's "Meet the Press," Biden also signaled he was open to legalizing gay marriage and said Secretary of State and former first lady Hillary Clinton has not decided whether to seek the presidency again in 2016.

"I think we may run as a team," he joked in the interview, stoking expectations that Clinton may be contemplating another run at the White House. "I don't know whether I'm going to run. And Hillary doesn't know whether she's going to run," he said.

The vice president, who has been a main point of contact with China for the Obama administration, said the United States expected China to stick to its commitment to let Chen go abroad and take up a fellowship at New York University.

"I think his future is in America," Biden said. "He has an opportunity to go to NYU ... and we're prepared to give (him) a visa right away. He's going to be able to take his family." Biden argued the United States' relationship with foreign powers including China, Russia and other countries have improved under President Barack Obama's leadership and said there could be some backsliding if Romney were elected.

Romney issued a warning about the risks of appeasing the United States' "No. 1 geopolitical foe" Russia after Obama was overheard telling Russian President Dmitry Medvedev in Seoul that he would have "more flexibility" to deal with contentious issues after the Nov. 6 election.

"If that's his prism through which he views our national security interest, I would say it would not be as strong," Biden said when asked whether the country would be less safe if Romney were president.

Pressed on social policy, Biden declined to specify whether the Obama administration would legalize gay marriage in a second White House term but said he personally was open to the change.

"The president sets the policy. I am absolutely comfortable with the fact that men marrying men, women marrying women and heterosexual men and women marrying one another are entitled to the same exact rights, all the civil rights, all the civil liberties," Biden said.

Obama has said his views on gay marriage were "evolving" but has also said individual states should set policy related to it.

The Democrat is not expected to advance legislation that could alienate independent voters ahead of November's election, and has not said whether legalizing gay marriage would be among his second-term priorities.

On Sunday, Biden also debunked rumors that Hillary Clinton may take his place as vice president on the 2012 Democratic ticket, saying: "there's no way out. I mean, they've already printed Obama-Biden." Meanwhile in China, Chen said Sunday he remained in a Beijing hospital but had asked government officials to help him apply to go abroad, after a deal between China and the United States.

"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 said in a brief telephone interview.

He added his injuries and limits on his movements by authorities had largely confined him to bed, making it difficult to leave the hospital to carry out the necessary procedures to leave the country.

Chen, 40, a self-taught lawyer, is at the center of a major diplomatic wrangle between China and the US after he dramatically escaped house arrest in the eastern province of Shandong and sought refuge at the US embassy in Beijing.

The activist was escorted to the Beijing hospital by US officials on Wednesday after being holed up inside the embassy for six days and said he wanted to leave China for his safety.

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

He is currently being treated for foot injuries sustained during his escape from house arrest. Speaking from his hospital bed, Chen said his foot was in a plaster cast.

His friends, he added, had been barred from visiting and US diplomats had only been allowed to see his wife, who was with him in the hospital.

"It's even difficult for me to get out of bed and my other friends cannot come, so I have no way," he said.

"They (US diplomats) have come, but they can't see me."