Activists on Tuesday urged democracies to speak out for the release of Chinese dissident Liu Xiaobo, fearing that pressure on Beijing has eased two years after he won the Nobel peace prize.

Around 30 supporters rallied outside the White House, carrying Liu's picture and holding a symbolic meal in his honor, with no food or wine served as a way to highlight the absence of the dissident and his wife Liu Xia, who is under house arrest.

Han Lianchao, vice president of Washington-based Initiatives for China, said that the pro-democracy advocacy group organized the event in hopes of keeping a spotlight on the world's only detained Nobel laureate.

"I don't think that Western democracies have done enough to free him. I think people tend to forget quite quickly," Han said.

The group held a similar event in Budapest and sent letters to Beijing-based ambassadors from democratic nations urging them to speak out on behalf of Liu and his wife.

"When history's pen writes about your time representing your country in China, you will want its ink to clearly underline your having made the case for Dr. Liu's release, rather than showing a stain of indifference," the letters said.

Liu is best known for spearheading a bold manifesto for democracy called Charter 08. Chinese authorities detained him in 2008 and sentenced him to 11 years in jail on Christmas Day 2009.

China responded furiously after the Nobel committee awarded Liu the prestigious prize and has retaliated diplomatically against Norway. Liu was represented by an empty chair at the award ceremony in Oslo.

President Barack Obama and other world leaders have urged China to free Liu and other prisoners, although the dissident's supporters fear that the spotlight has faded due to the time elapsed since the prize was awarded.

Jared Genser, the founder of the group Freedom Now and who serves as Liu's international counsel, said it was especially important to highlight human rights as China undergoes a leadership transition.

In an opinion piece he wrote for the The Huffington Post news website, Genser said China "missed an important opportunity" when Liu won the Nobel prize.

"The government's unfortunate response was a striking demonstration of its fear of domestic dissent combined with a willingness to engage in the type of international intimidation for which it so frequently criticizes other governments," Genser said.