The United States has renewed calls for China to free jailed dissident Liu Xiaobo who won the Nobel Peace Prize one year ago.

State Department spokeswoman Victoria Nuland made a new call Friday as the Nobel Prize committee announced new peace prize winners for this year. Nuland also urged Beijing to stop harassing Liu's wife and to “uphold Chinese international human rights obligations.”

Convicted for subversion in December 2009 after co-authoring a pro-democratic manifesto, Liu became the first Chinese citizen ever to win the prestigious Nobel peace award in October of last year.

He has been denied family visits during his three years in jail, and the government has placed his wife Liu Xia under house arrest without charge.

China director for Human Rights Watch Sophie Richardson says that during the past year, Liu Xia has been able to get online only once and that in a brief Twitter message she said her life was miserable, and that she and her family have been held hostage by the government.

Chinese authorities have prevented every attempt by journalists and diplomats to contact Liu Xia, either personally or by phone or the Internet.

Beijing has increased control over dissidents, and toughened security against any sign of a possible mass movement following a series of protests in the Arab world.