China Tuesday sentenced a rights activist to five years in prison after convicting him on subversion charges that supporters said were a pretext to punish him for investigating the deaths of thousands of schoolchildren in the 2008 Sichuan earthquake.

The court in the provincial capital, Chengdu, convicted Tan Zuoren of 'inciting subversion of state power' after he criticised the ruling Communist Party and circulated e-mails urging people to commemorate the party's military crackdown on democracy protesters in Beijing on June 4, 1989, his lawyers said.

But Tan's main lawyer, Pu Zhiqiang, and other supporters said officials had ordered Tan's arrest because he compiled a list of children who died in the earthquake and an independent report on the collapse of school buildings where many of the children died.

The court convicted Tan of subversion 'because he published stories about June 4 and he advocated commemorating June 4 by donating blood', Pu said by telephone from Chengdu.

Pu said the sentence was 'ridiculous and shameless'.

'His commemoration of June 4 and his expression of dissatisfaction with the June 4 massacre are within the range of freedom of speech (allowed by Chinese law),' he said. 'It can't be construed as a crime.'

Court officials in Chengdu declined to confirm the sentence.

In a statement released by supporters, Tan said he had 'no grounds to keep silent'.

'Facing the wrongdoings behind public power, facing the social danger behind bad decisions and special interests, I have no grounds to keep silent, and I will not run away,' Tan said in the statement.

'Where there are no mistakes, there are no dissenters,' he said. 'If there are no dissenters, there is no civil society.'

Another lawyer supporting him said Tan had prepared the statement to deliver at the end of his trial but judges prevented him from giving it.

Tan cooperated with other activists including Ai Weiwei, a leading Chinese artist and architect, who on Tuesday said the prosecution of Tan showed the government was 'intensifying the persecution of freedom of speech'.

'Tan Zuoren, today every one of 5,000 lonely souls is your child; they are all calling out for you,' Ai said in his blog on the popular website Twitter.

Poor construction is believed to have led to the collapse of many school buildings in the disaster, causing the deaths of 5,335 children, according to the government.

Tan, Ai and other activists listed 5,781 children who died while some parents claim the total number could exceed 10,000.

Tan estimated that more than half the children died as a result of poor construction of school buildings.

'Tan Zuoren is a writer with goodwill and conscience,' Ai wrote.

'If he is guilty, then China will never have independent thinking,' he said.

Ai underwent surgery in Germany late last year for a cerebral haemorrhage that he said was caused when he was beaten by police in Chengdu while he was supporting Tan during his trial in August.

Teng Biao, a leading human rights lawyer, also said the subversion charges against Tan had 'no legal grounds'.

'He uncovered the truth of the Sichuan earthquake and published it,' Teng said of Tan. 'He should have been praised rather than prosecuted.'

Tan is the second activist sentenced in Chengdu on charges linked to the death of children in collapsed school buildings during the earthquake, which killed at least 80,000 people.

In November, Huang Qi was sentenced to three years in prison for 'illegal possession of state secrets', a charge apparently linked to his reports of protests by parents of children killed in the earthquake.

The Chengdu City Intermediate People's Court rejected Huang's appeal against his sentence Monday, the Hong Kong-based China Human Rights Defenders reported.

An HBO film on the campaign by bereaved parents for an official account of their children's deaths, called 'China's Unnatural Disaster', was nominated in the short documentary category at next month's Oscars.

In an apparent reaction to the wave of public outrage over the hundreds of schools that collapsed during the quake, the government announced in May that school buildings nationwide must be reinforced to withstand earthquakes.