A U.N. human rights panel says China is violating international law by detaining dissident and Nobel Peace Prize winner Liu Xiaobo and his wife.

In an opinion published Monday, the U.N. Working Group on Arbitrary Detention says Beijing has not provided a sufficient justification for what it calls “interference with Liu Xiaobo's political free speech.”

Chinese authorities sentenced him to 11 years in prison in 2009 on subversion charges related to his co-authoring of a “Charter 08″ manifesto calling for political reforms and greater rights in Communist-ruled China.

Authorities placed his wife Liu Xia under house arrest last year, preventing her from traveling to a ceremony in Norway to accept the Nobel Peace Prize on his behalf.

The panel of independent rights experts from Chile, Norway, Pakistan, Senegal and Ukraine said Liu Xia has the right to be brought promptly before a judge and to be granted legal counsel. It called on the Chinese government to 'immediately release” her and her husband, and to provide them what it called “adequate compensation.”

U.S. State Department spokesman Mark Toner said Monday that Washington agrees with the U.N. panel's opinion that China must immediately release the couple from “arbitrary detention” and grant reparations.

China has vowed not to give in to international pressure to release Liu Xiaobo.