(Reuters) - The United States is "deeply concerned" about a crackdown on dissidents and rights lawyers in China, and the friction could impede the two powers' ties, Assistant Secretary of State Michael Posner said on Thursday after "tough" talks in Beijing.

The latest U.S.-China dialogue on human rights came at a contentious time, after China has jailed, detained or placed in secretive informal custody dozens of dissidents, human rights lawyers and protesters it fears will challenge Communist Party rule.

Posner told reporters after the two days of talks that he had raised the Obama administration's "deep concerns" about that crackdown, and he warned the broader relationship could suffer.

"We had a tough set of discussions," he told a news conference at the U.S. Embassy in Beijing.

"In fact, in recent months we've seen a serious backsliding on human rights, and a discussion of these negative trends dominated the human rights dialogue," he said.

"The most senior government officials of the United States are deeply concerned about the deterioration of human rights in China over the last several months," said Posner, who steers U.S. diplomacy about democracy, human rights and labor affairs.

The Obama administration would also discuss human rights at the annual Strategic and Economic in Washington D.C. next month, when top-level Washington and Beijing officials will talk about economic ties, currency issues and international security.

"Human rights is an essential feature of what we do, and so to the extent that there are serious human rights problems, those problems become an impediment to the relationship, and they make the other aspects of the relationship more difficult," said Posner.

China's leaders have become increasingly unyielding in the face of Western pressure over human rights issues, and say that those complaints amount to illegitimate meddling.

Beijing's alarm about dissent grew after overseas Chinese websites in February spread calls for protests across China inspired by the "Jasmine Revolution" of anti-authoritarian uprisings across the Arab world.

Since around that time, China has jailed, detained or placed in secretive informal custody dozens of dissidents, human rights lawyers and protesters it fears will challenge Communist Party rule.

They include the prominent artist-activist Ai Weiwei, who faces a police investigation on suspected economic crimes that his family has called an unfounded excuse for locking him up.

Posner said he raised the case of Ai, who is well-known abroad for his contemporary art and design.

"On that case, we certainly did not get an answer that satisfies," he said of Ai. "There was no sense of comfort from the response or the lack of response."

Chinese police have said Ai, a critic of China's ruling Communist Party, was under investigation for "suspected economic crimes." His family says the accusations are an unfounded excuse to silence him, and they have not heard directly from him since he was detained in early April.

U.S. officials also raised missing human rights lawyers, including Teng Biao; and Xue Feng, a U.S. citizen born in China who was jailed on controversial secrets charges, said Posner.

"Teng Biao's case is one that I'm particularly concerned about, because he has been missing for the last several weeks," said Posner.

"It's most unsettling and disturbing to, obviously, the families but to all of us when people simply disappear."


The mounting U.S.-China tensions over human rights carry echoes of 2010, when ties between the two countries were strained by arguments over Chinese Internet censorship; President Obama's meeting with the Dalai Lama, Tibet's exiled leader; and Beijing's outrage after the jailed Chinese dissident, Liu Xiaobo, won the Nobel Peace Prize.

Relations steadied after Chinese President Hu Jintao visited Washington for a summit in January this year. But Posner warned that human rights could become a sore spot.

"Inevitably, when there's been a deterioration, as there has been here, it makes the relationship that much harder," he said.

Secretary of State Hillary Clinton said earlier this month that she was "deeply concerned" about China's clamp-down and cited issues such as the detention of the Chinese artist and human rights activist Ai.

China's Foreign Ministry spokesman Hong Lei, speaking at a separate news briefing earlier on Thursday, said the human rights dialogue had been candid and in-depth.

"Both sides had frank and thorough exchanges on issues of mutual concern. Both sides said they were willing, on the basis of equality and mutual respect, to have dialogue," Hong said.

"At the same time we oppose the United States using human rights to interfere in China's internal affairs," Hong added, in a standard repetition of Beijing's stance.

(Additional reporting by Ben Blanchard; Editing by Don Durfee)