Vietnam is rejecting U.S. charges that dissident priest Nguyen Van Ly was returned to prison for expressing his opinions.

Foreign ministry spokeswoman Nguyen Phuong Nga said Thursday that the ailing Catholic priest was returned to prison Monday on the orders of a provincial court. She noted that Ly had been released on humanitarian grounds to receive medical treatment, but that the release was only temporary.

The U.S. government and human rights groups have criticized the latest arrest, arguing that Ly is still sick and that his original sentence was undeserved. The U.S. State Department said Wednesday that no one should be imprisoned for exercising the right to free speech.

The Vietnamese spokesman rejected that Thursday. She said that in Vietnam, no one is punished for expressing their opinions, only violators of the law are punished.

Father Ly has been a long-time critic of Vietnam's ruling communist government, and was sentenced to eight years in prison in 2007 for his pro-democracy activism. He was granted medical parole last year to receive treatment for a brain tumor and put under house arrest.

The medical parole expired at the end of March, but Ly was not immediately re-arrested. Vietnamese state media said he was re-arrested after he continued anti-government activities, such as criticizing the government's response to a maritime dispute with China.

Ly has spent more than 16 years in jail since the 1970s. He is one of the co-founders of the pro-democracy movement known as “Bloc 8406.”