US Representative Frank Wolf, a passionate campaigner for human rights causes whose advocacy took him to Tibet and Darfur, said Tuesday he would retire after serving 34 years in Congress.

The Republican lawmaker said he would not seek re-election next year in his district in Washington's Virginia suburbs, which have increasingly leaned toward President Barack Obama's Democratic Party, and would instead focus on his causes from outside government.

"As a follower of Jesus, I am called to work for justice and reconciliation, and to be an advocate for those who cannot speak for themselves," Wolf, 74, said in a statement.

"I plan to focus my future work on human rights and religious freedom -- both domestic and international -- as well as matters of the culture and the American family," he said.

Wolf has become known for his fiery denunciations of China, Vietnam, Sudan and other countries seen as violating human rights and has criticized the records of both Obama and his Republican predecessor George W. Bush. Earlier this year, he told AFP that Obama was "the worst president we have ever had" on human rights after he invited Vietnam's president for a rare visit to Washington.

In 2004, Wolf led the first delegation of US lawmakers to Sudan's western Darfur region and accused the Khartoum government of waging genocide against the largely black African population.

Wolf called on then UN secretary general Kofi Annan to do more in Darfur or resign, and later compared Bush's decision to go to the 2008 Olympics in China -- a supporter of Sudan -- to attending the 1936 Olympics in Berlin.

In 1997, Wolf slipped into Tibet as a tourist, not telling anyone he was a US congressman, after complaining about China's restrictions on foreign visitors. Wolf described his trip as a "nightmare tour," saying that China was carrying out a "cultural genocide" in the largely Buddhist region.

Wolf, using his position as chairman of a House of Representatives subcommittee in charge of science funding, in 2011 succeeded in barring NASA's cooperation with China's government and companies.

The clause caused controversy this year when NASA banned six Chinese scientists from a space conference, but the agency reversed course and Wolf stressed that his measure had not been meant to apply to individuals.

Wolf has also led charges that the Chinese technology company Huawei poses an espionage threat. His accusations recently led to the resignation of a senior intelligence official who had worked as a consultant to the firm.