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Dissident writer Yu Jie and his wife are prisoners in their apartment. Blocked by security agents outside their building, the couple have been living on deliveries of takeout food and groceries for nearly a month and voraciously reading books to stave off boredom.

The Yu family and scores of other activists are targets of one of the most extensive campaigns of surveillance, house arrest and other harassment by Chinese police against dissidents in years. The clampdown was brought on by the government's fury over the Nobel Peace Prize awarded to democracy campaigner Liu Xiaobo.

"We can't even take one step out of the apartment," Yu said in an e-mail Thursday from his home, where he and wife Liu Min have been held since Oct. 18. "Today we called the vegetable market for a delivery of food, and the guards actually came to our door to check every single item that was delivered."

"And no one is allowed to come to my place," Yu said. "Even a neighbor who tried to share some birthday cake was stopped by them."

In the sweep, police picked up democracy advocate Liu Shasha from her home before dawn Oct. 15 and drove her to her hometown 600 miles (965 kilometers) away. Constitutional scholar Zhang Zuhua, also under house arrest, said he was let out for lunch but had to dine with security agents. Human rights lawyers such as Pu Zhiqiang reported being followed by plainclothes officers.

The breadth of the police action underscores the authoritarian government's anxieties that the Nobel prize could unleash demands for political change.

Since the award was announced Oct. 8, state media have published scathing attacks on the Nobel committee and Liu, who is serving an 11-year prison sentence for co-authoring an appeal for democratic reform. The Chinese Foreign Ministry has leaned on European and Asian diplomats not to attend the Dec. 10 prize ceremony in Oslo.

The attention on dissidents, many of whom are among the thousands of signatories of Liu's Charter 08 appeal, appears aimed at ensuring they take no encouragement from the prize, while preventing them from traveling to Norway.

"The scale and the intensity of the monitoring and restrictions is definitely at an all-time high," said Nicholas Bequelin, Asia researcher for Human Rights Watch. "It's sort of an across the board, minute surveillance of all people who are deemed to be critics of the government."

In enforcing the clampdown, police actions have verged on the bizarre.

Police have barricaded the door to Yu's apartment building with a long table that is moved aside to allow other residents to come and go. Agents in a security office watch video footage of the couple's main door and windows, he wrote. Yu believes they are under house arrest because his wife helped Liu Xiaobo's wife buy thermal underwear for the jailed dissident.

The pair have had to cancel a trip overseas and apply for extended leave from work. Their mobile phone service has been cut, and their landline goes dead when reporters call or a politically sensitive topic arises. Police rejected their request to visit their 2-year-old son staying with his grandparents in western China.

Surprisingly, Yu noted, a book of Nobel Peace Prize winners' speeches that Yu ordered from Amazon China was not confiscated by the guards who checked the delivery.

Lawyer Teng Biao, whose passport was confiscated and who has been prevented from attending talks or gathering with friends, said activists are being watched more closely than in the weeks and months ahead of the 2008 Beijing Olympics — when police also launched an extensive dragnet to pre-empt any trouble.

The Nobel prize winner's wife, Liu Xia, also remains under house arrest and has lost contact with the outside world since late October when she was last in touch with friends, said Yang Jianli, an exiled Chinese democracy activist and close friend of the couple.

The activist network, Chinese Human Rights Defenders, said it has received about 100 reports of people being harassed, surveilled, interrogated, detained or placed under "soft detention" — virtual house arrest — across the country.

Outside the scholar Zhang's apartment, guards are posted at all hours and sleep in the hallway at night.

Liu Shasha, a rights activist who protested in front of three Beijing police stations in support of Liu, said four men and a woman in plainclothes stormed into her apartment in Beijing at 4 a.m. on Oct. 15, seized her mobile phone and laptop and ordered her to follow them.

"I was dragged out of the door and didn't even get time to dress properly. I was still wearing slippers on my feet. They threatened to seal my mouth with a towel and a roll of adhesive tape if I kept shouting," Liu Shasha said by phone from her home in Henan province, where she was driven by security agents.

Bequelin said the clampdown has put on display China's wide array, and growing use, of tactics for controlling dissent.

Rights lawyer Gao Zhisheng, for example, has repeatedly disappeared and was last seen in April shortly after announcing he was abandoning his role as a government critic. Blind activist lawyer Chen Guangcheng was released from prison after four years in September, only to find himself immediately under house arrest.

"You effectively silence activists without attracting the attention and opprobrium that accompanies arrests and imprisonment," Bequelin said. "Over the past two or three years we really have seen an increase in the array of unlawful measures taken against dissidents."

The Beijing public security bureau did not immediately respond to a faxed list of questions.