US lawmakers have urged President Barack Obama to speak up to China to ensure the safety of two prominent dissidents, one of whom is a favorite to win the Nobel Peace Prize.

Thirty lawmakers asked Obama to raise the cases of writer Liu Xiaobo, thought to be in contention when the Nobel is announced Friday, and human rights lawyer Gao Zhisheng, when he meets next month with Chinese counterpart Hu Jintao."

We write to ask that you urge President Hu to release two emblematic Chinese prisoners of conscience, Liu Xiaobo and Gao Zhisheng," 29 of the House members across party lines wrote in a letter released Wednesday.

In a separate message, Representative Ileana Ros-Lehtinen, the top Republican on the House Foreign Affairs Committee, pressed Obama to seek the dissidents' "unconditional release."

"Your personal attention to Dr Liu and Mr Gao's detentions could be instrumental in securing their freedom," she wrote.

Obama is expected to meet his Chinese counterpart on the sidelines of the November 11-12 summit of the Group of 20 major economies in Seoul, South Korea.

Liu, 54, was jailed for 11 years in December on subversion charges after co-authoring "Charter 08," a bold call for democratic reform that was signed by hundreds of Chinese after it was circulated on the Internet.

China's foreign ministry last week warned that Liu was not suited for the Nobel Peace Prize as he was "sentenced to jail by Chinese judicial authorities for violating Chinese law."

Gao, who has taken up some of China's most sensitive cases such as underground Christians and the Falungong spiritual movement, has gone missing twice since last year. His family has escaped to the United States.

Gao's wife, Geng He, said she last spoke by telephone with him in April.

"I have absolutely no idea where he is now," Geng, who lives in California with their 17-year-old daughter and seven-year-old son, told AFP.

"I'm very, very worried. I know from past experience that every time he disappears, it's usually tragic -- he is under close monitoring or suffers a lot of torture," she said.

Geng said that she and her son barely recognized Gao when they saw pictures of him this year before he again vanished. In their last conversation, she said she asked Gao to see a dentist.

"I told him that it looked like he had aged 20 years. His teeth looked so bad and black and I asked if he could go see a dentist," she said.

Geng appealed to the United States and other nations to keep pressing on her husband's case.

"Gao's life and safety can only be guaranteed if the international community keeps up the pressure on the Chinese government," she said.

In their letter, the members of Congress voiced concern that China was putting growing pressure on human rights lawyers.

"We strongly believe that the United States government and international community must not allow China to continue to cross this line," the lawmakers wrote.

"If lawyers are hauled away for the 'crime' of defending their clients, then even the pretense of rule of law in China has failed," they wrote.

Obama has sought to broaden relations with a growing China on issues ranging from climate change to the global economy. His administration has claimed success, with China last week agreeing to resume military ties with Washington.

But human rights activists have accused the administration of downplaying human rights. In a break with past practice, China did not release any dissidents when Obama paid his maiden visit to Beijing last year.

(Source: AFP)