The United States said Thursday it was ready to help Chinese dissident Chen Guangcheng if he sought exile, after the blind activist expressed fears for his safety and pleaded to be taken abroad.

The fate of the campaigning lawyer-dissident, who escaped from house arrest and spent six days at the US embassy in Beijing up until Wednesday, overshadowed the opening of top-level Chinese-US talks in Beijing.

The details of why Chen left the embassy remained unclear. US officials said he left after Beijing pledged he and his family would be treated "humanely".

But US-based rights group China Aid said the activist "reluctantly" left the embassy after Chinese authorities threatened his family.

Speaking to AFP on Thursday, Chen said he did not initially want to seek asylum overseas but changed his mind after emerging from the embassy due to concern for his safety and that of his family.

"I want to go overseas. I want the US to help me and my family. They helped me before," he said by phone from a Beijing hospital where he is being treated for a foot injury suffered during his dramatic escape on April 22.

"I don't feel safe here. I want to leave."

A senior US official said that Washington was ready to help Chen but declined to comment on whether the United States would assist him in seeking asylum, saying that Chen's position was unclear.

Top US officials were in the process of speaking to Chen, along with their Chinese counterparts, to determine what the activist wants, the official said on condition of anonymity.

In an interview with CNN, the 40-year-old Chen said since his escape his wife had been tied to a chair for two days by police in his home province of Shandong, in northeastern China, who threatened to beat her to death.

The activist, who riled Chinese authorities by exposing forced abortions and sterilisations under the government's "one-child" policy, appealed directly to US President Barack Obama to get him and his family out of China.

He also accused US embassy officials of pushing him hard to leave the safety of the embassy, where he had sought refuge for six days after fleeing his home. But US ambassador Gary Locke insisted that Chen had made a voluntary choice to leave and never requested asylum and that the activist was not pressured to leave the embassy.

Chen's flight came despite round-the-clock surveillance at his house in Shandong, where he has alleged that he and his family suffered severe beatings after he ended a four-year jail term in 2010.

During Chen's house arrest, US Secretary of State Hillary Clinton led international calls for his release, and she spoke to him on Wednesday after arriving in Beijing to attend the high-level "Strategic and Economic Dialogue".

At Thursday's opening of the two-day meeting, Clinton did not single out Chen, but told her Chinese hosts including President Hu Jintao that they cannot deny the "aspirations" of their citizens "for dignity and the rule of law".

However, in his own opening remarks, Hu called for the United States and China to respect each other's concerns and warned that any worsening of relations posed "grave" risks for the world.

Clinton on Wednesday said the United States remained "committed" to Chen and US officials said they had received assurances from China that the legal campaigner could be safely reunited with his family.

Assistant Secretary of State Kurt Campbell said he had spent 30-40 hours in conversation with Chen during his stay at the US embassy, and at all times the activist was eager to return to "a more normal life in China".

"Never once did he talk about asylum or coming to the United States," Campbell told NPR radio in the United States from Beijing.

"And I think he fully recognises what are some of the challenges that people who come to the United States in these circumstances face," he said, before Chen made his public appeals for shelter abroad.

Despite Wednesday's agreement, Beijing demanded that the United States apologise for what it called "interference" in its affairs.

No apology has been forthcoming from Washington, but Campbell said Chen's flight to the embassy presented "an extraordinary circumstance with very unusual parameters, and we don't expect it to be repeated".

Any renewed abuse against Chen could prove to be a political nightmare for Obama's administration, which has faced calls to show its commitment to defend human rights in China as the US president runs for re-election.