China blocked European officials from meeting with the wife of the imprisoned Nobel Peace Prize winner, cut off her phone communication and kept her under house arrest _ acting on its fury over the award.

As China retaliated, U.N. human rights experts called on Beijing to free democracy campaigner Liu Xiaobo from prison. Liu, a slight, 54-year-old literary critic, is in the second year of an 11-year prison term after being convicted of inciting subversion.

He was permitted a brief, tearful meeting in prison with his wife Sunday and said dedicated the award to the "lost souls" of the 1989 military crackdown on student demonstrators.

In naming him, the Norwegian-based Nobel committee honored Liu's more than two decades of advocacy of human rights and peaceful democratic change _ from demonstrations for democracy at Beijing's Tiananmen Square in 1989 to a manifesto for political reform that he co-authored in 2008 and which led to his latest prison term.

On Tuesday, U.S. officials said they were closely following the situation of Liu's wife, Liu Xia. "We remain concerned by multiple reports that Liu Xia is being confined to her home in Beijing," an U.S. Embassy spokesman, Richard Buangan, wrote in response to questions. "Her rights should be respected, and she should be allowed to move freely without harassment."

The Beijing public security bureau and the foreign ministry had no immediate comment on why authorities were apparently restricting her movements since she has not been charged with anything. But "soft detention" is a common tactic used by the Chinese government to intimidate and stifle activists and critics.

Beijing reacted angrily to Friday's announcement awarding the Nobel Peace Prize to Liu, calling him a criminal and warning Norway's government that relations would suffer, even though the Nobel committee is an independent organization. On Monday, it abruptly canceled a meeting that had been scheduled for Wednesday between visiting Norwegian Fisheries Minister Lisbeth Berg-Hansen and her Chinese counterpart.

European diplomats were prevented from visiting Liu's wife, Liu Xia, who has been living under house arrest since Friday. Liu Xia has been told that if she wants to leave her home, she must be escorted in a police car, the New York-based group Human Rights in China said.

She has reported that her phone communications, along with her Internet, has been cut off; both her and her brother's mobile phones have been interfered with, HRIC said.

Simon Sharpe, the first secretary of political affairs of the EU delegation in China, said he went to see Liu Xia at her home in Beijing to personally deliver a letter of congratulations from European Commission President Jose Manuel Barroso.

Sharpe was accompanied by diplomats from 10 other countries, including Switzerland, Sweden, Poland, Hungary, the Czech Republic, Belgium, Italy and Australia.

But three uniformed guards at the gate of Liu's apartment complex prevented the group from entering.

"We were told that we could only go in if we called somebody from the inside and if they came out to meet us. But of course, we can't call Liu Xia, because it's impossible to get through to her phone," Sharpe told reporters at the entrance to the compound.

The Nobel Committee has sent the official prize documents, including an invitation to the Dec. 10 ceremony, to the Chinese Embassy in Oslo, asking Chinese authorities to hand them over to Liu, said committee secretary Geir Lundestad.

In recent days, Beijing has also stepped up its harassment of other activists, detaining several when they tried to organize a dinner to celebrate Liu's Nobel.

Zhang Jiannan, who runs an Internet forum on political matters, told The Associated Press that he and other activists had gone out Friday to celebrate Liu's victory. He was placed under house arrest Saturday and warned by police not to participate in political activities.

On Monday, lawyer Pu Zhiqiang was the latest to be detained by police, according to his assistant, who did not want to be identified. Pu had sent out a message via Twitter on Sunday that said security officials had showed up telling him not to accept interviews with foreign media.

Meanwhile, the Dalai Lama criticized China for its response to the Nobel Peace Prize award, saying the government "must change," the Kyodo News agency reported. The Tibetan spiritual leader, who won the prize himself in 1989, said Beijing must recognize that fostering an open society is "the only way to save all people of China."

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Associated Press Writers Gillian Wong, Ken Teh, Isolda Morillo and researcher Xi Yue in Beijing, Bjoern H. Amland in Oslo, Norway and Louise Nordstrom in Stockholm contributed to this report.