A Chinese court has handed an 18-month jail term to a man who applied to hold a protest on the anniversary of the 1989 Tiananmen Square killings, his lawyer said.

On Monday, Gu Yimin was found guilty of "inciting state subversion" for posting pictures of the 1989 crackdown online and applying for permission to stage a protest on its anniversary last year, his lawyer Liu Weiguo .

"This judgement violates the constitution," the AFP news agency quoted Liu as saying. He added that Gu would appeal the verdict, handed down by a court in Changshu in the eastern province of Jiangsu.

"We maintain that Gu Yimin was exercising his right to freedom of speech."

Liu said that men he believed to be state security officers had assaulted him and another lawyer outside the courthouse.

Hundreds of protesters were killed in 1989 when the Chinese army cracked down on their pro-democracy movement in Tiananmen Square in Beijing, the symbolic heart of the Chinese state.

Gu applied to local authorities to hold a small-scale protest on June 4 last year, the 24th anniversary of the event, his wife Xu Yan previously told AFP news agency.

He stood trial in September and denied the charges, his lawyer said at the time, adding that Gu, 36, had called off his protest when authorities warned him not to go ahead.

"There is nothing illegal about posting a photograph of a genuine incident," Liu said. "If his activities caused damage to the [Communist] party, that's not the same as damaging the state."

The Communist party remains intolerant of dissent and tightly censors public discussion of the crackdown. The vaguely defined charges of incitement to state subversion have previously been used by the ruling party to imprison political opponents.

Nobel prize winner Liu Xiaobo was sentenced to 11 years in jail on subversion charges in 2009 after circulating a petition calling for political reforms including democratic elections.