BEIJING » China is pressing European governments to boycott the ceremony awarding the Nobel Peace Prize to Chinese dissident Liu Xiaobo, warning that the award interferes in China’s internal affairs and that Liu is a criminal, Western diplomats said Thursday.

Beijing also urged governments not to issue the statements of support and congratulation that are customary for Nobel laureates, they said.

The unusual request was delivered to European embassies in Oslo, the site of the award ceremony in December, in a written demarche, or diplomatic note, the highest level of communication between diplomatic outposts. How many embassies received the note was unclear.

Liu, a Beijing author and intellectual, was convicted of subversion and sentenced to 11 years in prison last year for his role in writing Charter 08, an Internet manifesto that calls for democratic reforms and an end to the Communist Party’s monopoly on power.

The police detained him shortly before the document was issued in December 2008, and he has remained in custody since. His wife, Liu Xia, is under constant guard in the couple’s Beijing apartment.

Whether by Beijing’s design or otherwise, the Nobel award is emerging as an early test of China’s newfound diplomatic clout, the product of its emergence as a global economic power.

China is investing heavily in Europe, buying debt and assets depressed by the global financial crisis and becoming a significant partner for hard-hit nations like Spain and Greece. Britain is sending its largest ever ministerial delegation, including Prime Minister David Cameron, to Beijing next week in search of business deals. President Hu Jintao of China visited France on Thursday, apparently to purchase 110 Airbus passenger jets for Chinese airlines.

Since the October announcement of the Nobel award, the United States and other governments have urged China to free Liu, while some governments, including some Western democracies, have pointedly limited their statements to congratulations without calling for his release.

Chinese officials have attacked the Nobel award committee, insisting that the award demeans the peace prize. China’s state-controlled media have published polls purporting to reflect Chinese citizens’ unhappiness with the award, and newspapers have defended China’s human rights record while assailing those of the United States and other nations.

Beijing also warned Norway before the prizewas announced that naming Liu would strain diplomatic relations. In recent days, Chinese officials have also called foreign diplomats to meetings to deliver warnings similar to those in the diplomatic note, The Associated Press reported.

In an interview Thursday, one European diplomat in Beijing called the demands undiplomatic but not particularly surprising.

"You could expect it, because if you look at their reaction, it’s been really unreasonable," said the diplomat, who spoke on condition of anonymity, citing diplomatic protocol. "It’s not something that looks very good, but it’s something that it seems they cannot understand."

Since the award was announced, Chinese authorities have intensified a crackdown on political and human rights activists, detaining some and placing others under tight surveillance. Liu’s wife publicly invited scores of Chinese activists and celebrities to attend the Oslo ceremony, but it is widely expected that the government will bar them and her from leaving the country.

Yu Jie, a Beijing writer and one of Liu Xiaobo’s close friends, said in an interview five days ago that domestic security officers were preventing him and his wife from leaving their apartment. He said that the couple’s cell phone service had been halted and that three video cameras had been installed on the building opposite their apartment.

Although security officers refuse to explain their mission, Yu said he believed "they are afraid we are going to Oslo for the award ceremony."

"The situation is getting really bad," he said.

Pu Zhiqiang, a human-rights lawyer, said he had been under surveillance since Liu’s award was announced.

"They know they don’t have any legal grounds for this," he said. "But they fear nothing."

Nicholas Bequelin, a researcher for New York-based Human Rights Watch, said the government was nervous about figures like Pu and Yu because they "are people who can spread the news within Chinese society."

"The police know these people are not going to cause the collapse of the Communist Party," Bequelin said, "but this is all about information control. These are activists who sense that this is a historic moment and want to make the most of it."

Even some obscure people appear to have been swept up in the crackdown. News agencies reported that Guo Xianliang, an engineer, disappeared while on a business trip in Guangzhou after handing out fliers about the peace prize. Guo is not a well-known activist, the reports said, but may have provoked the ire of authorities by calling attention to Liu’s imprisonment.