DUBAI — A prominent Bahraini opposition activist was sentenced to three years in jail on Thursday for anti-government protests, his lawyer said, a verdict that rights campaigners said showed the absence of political reform on the island.

Bahrain has been in turmoil since pro-democracy protests led by its Shiite Muslim majority erupted last year. Washington has called on its ally to talk to the opposition.

Nabeel Rajab is the founder of the Bahrain Centre for Human Rights and has led many protests against the wide powers of the Sunni Al Khalifa dynasty which rules the island kingdom.

A hero to protesters, but villain for those Bahrainis who fear the protests will bring Shiite Islamists to power, Rajab was already serving three months in jail over a tweet criticising the prime minister. A court said it insulted Bahrainis.

The judge ruled in three cases on Thursday, all related to participating in peaceful protests, and handed Rajab a one-year jail sentence for each, said Mohammed Jishi, adding that he planned to appeal.

“It is a very stiff and unexpected ruling, I am surprised. They are peaceful protests, not violent ones,” Jishi said.

Others found guilty in similar cases, Jishi said, had been sentenced to six months at most and some were freed on bail.

EU foreign affairs representative Catherine Ashton issued a statement expressing concern at the verdict for charges that she said were merely Rajab exercising his fundamental freedoms.

“The High Representative expects that this sentence in Mr Rajab’s case will be reconsidered in the appeal process,” it said. “Fair and impartial justice is a key requirement to overcome the current challenges in Bahrain.”

The government’s Information Affairs Authority said the charges against Rajab had been related to violence.

Public prosecutors had said Rajab’s participation in marches and “provocation of his supporters” led to violence, including throwing petrol bombs and blocking roads.

Rights groups including Human Rights First, Front Line Defenders and Index on Censorship sharply criticised the ruling. Amnesty International said it was a “dark day for justice”.

“Like many others in Bahrain, Nabeel Rajab is a prisoner of conscience, jailed solely for peacefully exercising his right to freedom of expression and assembly. He should be released immediately and his convictions and sentences quashed,” said Amnesty’s Hassiba Hadj Sahraoui in a statement.