China hit back on Tuesday at critics of its human rights record, saying the world was using the Olympics, which Beijing will host in August, as an excuse to make a villain out of its government.

Rights groups have condemned the arrest of activist Hu Jia last month on charges of inciting to subvert the government, but Foreign Ministry spokeswoman Jiang Yu rejected accusations that China was cracking down ahead of the Games.

"On the contrary, some organisations and individuals take the Olympics as an opportunity to play up some subjects as a way to vilify China," Jiang told a regular news conference.

"We resolutely oppose that because it violates the spirit of the Olympics."

But the criticism is not only coming from foreign watchdogs.

A group comprising dozens of Chinese lawyers, academics, editors and writers signed an open letter condemning Hu's arrest and urging the government to improve its human rights record ahead of the Games.

Hu, 34, first came to prominence over his advocacy for AIDS sufferers. He has since closely followed the trials of human rights lawyer Gao Zhisheng and civil rights campaigner Chen Guangcheng among others, e-mailing regular updates on their cases to reporters.

Police have also prevented Hu's wife, fellow activist Zeng Jinyan, their newborn baby and Zeng's elderly mother from leaving the couple's Beijing home.

Jiang defended China's justice system.

"The Chinese government, according to law, protects the freedoms and other rights of Chinese citizens," she said. "Only if you violate the law will you be punished by the law."

Jiang also criticised reports that Chinese authorities have been forcing Tibetans to sign a petition opposing the return of the Dalai Lama, the exiled spiritual leader of Tibetan Buddhism who China considers a traitor.

"Some Tibetan indepedence forces are engaged in anti-China and separatist activities," she said.

"The Dalai Lama has always been engaged in separatist activities under the guise of religion."

The Dalai Lama has lived in exile in India since fleeing Tibet in 1959 after a failed uprising against Chinese rule, but many in ethnic Tibetan regions of western China still revere him as a spiritual leader and hope for his return.