Chinese activist Chen Guangcheng on Wednesday "reluctantly" left the US embassy where he had sought protection after fleeing house arrest, following a deal with Beijing, a US-based rights group said.

China Aid said it had been told by "reliable sources" that Beijing had made threats against relatives of the legal campaigner.

This came despite US officials saying hours after US Secretary of State Hillary Clinton arrived in China for pre-arranged talks that Beijing had pledged Chen and his family would be treated "humanely" and moved to a safe place.

Victoria Nuland, State Department spokeswoman, denied threats were made, but said Chinese officials made clear Chen's family would be returned to their home in the eastern province of Shandong -- where they suffered repeated abuse -- if he remained at the embassy.

China Aid said in a statement: "Chen's decision for departure from the US embassy was done reluctantly because 'serious threat to his immediate family members were made by Chinese government' if Chen refuses to accept the Chinese government's offer.

"We are deeply concerned about this sad development if the reports about Chen's involuntary departure (from US embassy) is true," added the group, run by the exiled Chinese activist Bob Fu, who has been in close touch with Chen and his supporters.

Zeng Jinyan, wife of the dissident activist Hu Jia, who met with Chen after his dramatic flight from house arrest, also claimed that Chen "did not want to leave the embassy", citing the wife of the blind campaigner.

Chen, who riled Chinese authorities by exposing forced abortions and sterilisations under the "one-child" policy, fled house arrest on April 22 and sought refuge in the US embassy, where he demanded assurances on his freedom.

In a video address to Premier Wen Jiabao released after his dramatic escape, the blind activist alleged he and his wife and young child had suffered repeated abuses at the hands of local officials in his hometown in northern China.

Clinton said the United States remained "committed" to the 40-year-old legal campaigner, whose treatment she has repeatedly criticised in the past.

"Mr. Chen has a number of understandings with the Chinese government about his future, including the opportunity to pursue higher education in a safe environment. Making these commitments a reality is the next crucial task," she said in a statement.

"The United States government and the American people are committed to remaining engaged with Mr. Chen and his family in the days, weeks and years ahead."

But responding to a question on Clinton's statement, China's foreign ministry spokesman Liu Weimin said: "What the US needs to do is to stop misleading the public and stop making every excuse to shift responsibility and conceal its own wrongdoing."

He said the US should not "interfere" in China's domestic affairs and urged it to "take necessary measures to prevent a similar incident".

Chen spoke to Clinton by telephone soon after he left the embassy for a nearby hospital, where he was treated for an injury sustained during his escape and reunited with his family, a senior US official said.

"After saying in Chinese how grateful he was that she had mentioned him in the past and supported his case, he said in broken English, 'I want to kiss you'," the official told reporters on condition of anonymity.

US officials also said that Chen never sought passage to the United States and instead wanted to live and work in China alongside his family.

A US friend of Chen's involved in the negotiations said the activist agreed to leave the embassy after receiving assurances President Barack Obama would publicly back the deal.

"We made a condition of acceptance that President Obama himself show his interest and state the US support for the arrangement and I'm sure Obama, in the light of the campaign, will soon have an opportunity to take that position," Jerome Cohen of the Council on Foreign Relations told reporters.

Any renewed abuse against Chen could prove to be a political nightmare for President Barack Obama's administration, which has faced calls to show its commitment to safeguard human rights in China.

The case had threatened to overshadow the annual meeting between leaders of the world's two largest economies on key issues ranging from North Korea's rocket launch to Syria.

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

"China is very unhappy over this. The US action is an interference in China's internal affairs and China cannot accept it," Chinese foreign ministry spokesman Liu said.

A US official said there would be no repeat of the incident, but declined to comment on China's call for an apology.

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

In the video released after his escape, he appealed to Wen to punish several local officials he said had made his family's life a misery.

Before the Chen case, Washington had hoped to showcase small signs of progress in relations with China at the Strategic and Economic Dialogue, which also includes US Treasury Secretary Timothy Geithner.

Largely in response to inflationary pressure, China has let its yuan appreciate. Currency levels have long been a source of friction, with US lawmakers charging that Beijing keeps the value of the yuan artificially low to flood the world with cheap exports.

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