A top Chinese human rights lawyer detained for more than a year was criminally charged Friday over comments he made online, officials said, prompting denunciations from the United States and advocacy groups.

Pu Zhiqiang, a celebrated rights campaigner who has represented dissident artist Ai Weiwei, was taken into detention last May in the run-up to the 25th anniversary of the Tiananmen Square killings.

Pu, 50, was accused of "inciting ethnic hatred" and "picking quarrels and provoking trouble," for comments made on the Twitter-like microblogging service Sina Weibo, Beijing prosecutors said online.

The charges, which carry maximum jail sentences of 10 and five years respectively, are said by his legal team to stem from 28 posts he wrote on the service.

They include posts questioning a state media account of a "terrorist" attack in the mainly Muslim region of Xinjiang, and another accusing the ruling Communist Party of "lying".

Pu is virtually certain to be convicted. The party keeps a close grip on the court system and according to official figures 99.93 percent of defendants in Chinese criminal trials are found guilty.

A US State Department spokesman expressed "deep concern" for the lawyer and called for his immediate release, describing Pu's treatment as evidence of wider state intolerance of dissidents in China.

"His indictment appears to be part of a systematic pattern of arrests and detentions of public interest lawyers, Internet activists, journalists, religious leaders and others who challenge official Chinese policies and actions," Jeff Rathke said.

British-based campaign group Amnesty International called for authorities to "end their persecution" of Pu.

"He did nothing more than comment on current affairs on social media. The Chinese government is blatantly violating his freedom of expression and attempting to silence an independent voice," Amnesty researcher William Nee said in a statement.

China's foreign ministry earlier this month dismissed US calls for Pu's release, saying that Washington should "concentrate on its own domestic problems".

Pu was previously celebrated in China's state-run media for seeking compensation for people sent to "re-education through labour" camps. The government said in 2013 it would abolish the system.

- 'Inhumane torture' -

Beijing prosecutors said on a verified Sina Weibo account that "Pu Zhiqiang used information networks to send many Weibo posts inciting ethnic hatred".

Pu "insulted others, disrupted public order and shall be held criminally responsible," the statement continued.

Pu, who is diabetic, has been subjected to harsh treatment by the authorities during his year in detention, according to a letter written by his wife in December.

"He is suffering from... high blood pressure, hyperlipidemia and heart disease," Meng Qun wrote in the letter.

"He was interrogated for almost 10 hours every day during the first three months in the detention centre... (and) he was subjected to inhumane torture both physically and mentally."

Chinese authorities routinely round up outspoken critics of the Communist Party in the weeks before dates they deem sensitive, such as the June 4 Tiananmen anniversary, and Pu was held after attending a private seminar about the crackdown.

More than 40 journalists, lawyers, scholars and activists were held under various forms of detention ahead of last year's anniversary, Amnesty International said, in a larger clampdown than usual.

He was formally arrested in June for "creating disturbances and illegally obtaining personal information," charges his legal team said were aimed at silencing the government critic.

Meanwhile a wider crackdown on dissent has been under way since Chinese President Xi Jinping took office two years ago, with scores of government critics detained and dozens jailed.