In this April 5, 2018 photo, prominent human rights lawyer Nguyen Van Dai, center, and defendant Nguyen Bac Truyen listen to the verdict at a trial in Hanoi. Nguyen Van Mieng, the lawyer for prominent human rights lawyer Nguyen Van Dai said he was sentenced to 15 years in prison and five years of house arrest while his fellow activists received sentences from seven to 12 years at the one-day trial Thursday. (Vietnam News Agency via AP)

HANOI, Vietnam - Six human rights activists were sentenced to harsh prison terms in Vietnam after being convicted of attempting to overthrow the government by advocating a multiparty democracy.

Prominent human rights lawyer Nguyen Van Dai received the most severe penalty of 15 years in prison and five years of house arrest at the one-day trial Thursday, said his lawyer Nguyen Van Mieng. The others received sentences from seven to 12 years.

They were charged with affiliating with a group called Brotherhood for Democracy, whose purpose was to change the leadership of the Communist Party and build a multiparty system.

"The sentences are too harsh to the defendants," Mieng said. "They fought for human rights, they fought for the rights of multi-party system ... which are recognized achievements of mankind, but the court sees it as serious (threat) to the regime."

Five of the defendants including Dai maintained they were innocent because what they did was right, Mieng said. One defendant confessed to the crime and got the most lenient sentence, he added.

"The purpose of the group is to change the leadership of the Communist Party of Vietnam, build a multi-party system," the official Vietnam News Agency quoted the verdict as saying. "The defendants' act is not fight for democracy, but acts that aim at overthrowing the people's administration."

"The defendants' act is especially serious because it directly impacts the survival of the people's administration," it said.

Prosecutors identified Dai as the mastermind of the group who recruited members and sought financing from foreign organizations and individuals, which totalled more than $80,000, VNA reported earlier.

Dai and four others had previously been jailed for violating national security laws, and Dai's license to practice law was revoked.

State Department spokeswoman Heather Nauert said the United States was deeply troubled by the harsh sentences under a "vague charge" and called for the release of all "prisoners of conscience" immediately.

"Individuals have the right to the fundamental freedoms of expression, association, and peaceful assembly, both online and offline," she said in a statement. "The United States is deeply concerned by the Vietnamese government's efforts to restrict these rights, through a disturbing trend of increased arrests, convictions, and harsh sentences of peaceful activists."

Speaking to reporters at a regular briefing Thursday, Vietnamese Foreign Ministry spokeswoman Le Thi Thu Hang said there are no "prisoners of conscience" in Vietnam and no one has been arrested for freedom of expression.

"In Vietnam, like other countries in the world, all acts that violate the laws are seriously dealt with in accordance with law," she said.

Amnesty International says 97 people are serving jail sentences for violating national security laws in Vietnam, while Human Rights Watch counts 119.

News from © The Associated Press, 2018