The US ambassador to Beijing said that China's human rights record was deteriorating as its communist rulers feel threatened in the wake of pro-democracy uprisings across the Middle East.

"The human rights climate has always ebbed and flowed in China, up and down, but we seem to be in a down period and it's getting worse," Ambassador Gary Locke told "The Charlie Rose Show" on US public television late Monday.

Locke pointed to China's detentions of dissidents, lawyers and other perceived critics since the onset of the "Arab Spring" which toppled authoritarian leaders in Egypt, Libya and Tunisia last year.

"The Chinese leaders are very fearful of something similar happening within China," Locke said.

"So there's been a significant crackdown on dissension, political discussion, even the rights and the activities of lawyers who advocate on behalf of people who have been poisoned from tainted food and medicines."

The ambassador was back in Washington for consultations ahead of a visit next month by Chinese Vice President Xi Jinping, who is widely expected to take the helm of the rising Asian power in early 2013.

Locke's trip comes after Treasury Secretary Timothy Geithner visited China and Japan in an effort to encourage Asia's energy-hungry top economies to cut imports from Iran due to worries about the Islamic republic's nuclear program.

Locke acknowledged that China, while supporting previous UN sanctions on Iran, has yet to be convinced of the need for further punitive measures.

"The United States government is most concerned about Iran's nuclear capability and we really feel that more pressure must be put on Iran," Locke said.

"I don't believe that they think that Iran poses an immediate threat," he said.

Foreign ministry spokesman Liu Weimin said last week that China's energy needs were "reasonable" and should not be linked to the Iranian nuclear issue.

Iran has threatened to cut off access to the Gulf in anger at a new US law that targets foreign consumers of its oil and European Union proposals for an oil embargo.

Iran insists that its sensitive uranium enrichment work is for peaceful purposes, but Western powers suspect it is building nuclear weapons.