By Andrew Hammond and Rania El Gamal
DUBAI (Reuters) - A prominent Bahraini opposition activist was sentenced to three years in jail on Thursday for anti-government protests, his lawyer said, a verdict Washington said was deeply troubling and rights campaigners called a "dark day for justice".
Bahrain, the base of the U.S. Navy's Fifth Fleet, has been in turmoil since pro-democracy protests led by its Shi'ite 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 Shi'ite Islamists to power, Rajab was already serving three months in jail over a tweet criticizing the prime minister. A court said it insulted Bahrainis. An appeal hearing is due next week.
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 lawyer Mohammed al-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.
U.S. State Department spokeswoman Victoria Nuland said her government had contacted Bahrain over the verdict. "We've long made clear that it's critical for all governments, including Bahrain, to respect freedom of expression, freedom of assembly," she said. "So we are deeply troubled by the sentencing today."
EU foreign affairs High Representative Catherine Ashton issued a statement expressing concern at the verdict, saying Rajab was merely exercising his fundamental freedoms and that she expected the sentence to be reconsidered on appeal.
The Bahrain government's Information Affairs Authority (IAA) 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.
The IAA statement quoted a prosecution official who said there was evidence Rajab incited "violence and escalation against law enforcement officers, resulting in deaths".
It was not clear what deaths the official was referring to, but many protesters and residents have died due to clashes since martial law ended in June last year - opposition parties put the figure at more than 45.
Rights groups have blamed police for what they say is excessive use of force including heavy use of teargas. The government disputes the causes of death.
The interior ministry says police, who do not used live fire in the confrontations, are practicing restraint and that more than 700 officers have been wounded in clashes.
Rights groups including Human Rights First, Front Line Defenders and Index on Censorship sharply criticized 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," Amnesty's Hassiba Hadj Sahraoui said in a statement. "If anything, this latest verdict marks the end of the facade of reform in Bahrain."
There has been little progress towards opposition demands for reforms including a parliament with full powers to legislate and form governments. Many Shi'ites complain of political and economic marginalization, a charge the government denies.
The Al Khalifa family has increased parliament's powers of scrutiny over ministers and says it is reforming policing to conform with international standards.
While uprisings overthrew long-standing governments in Egypt, Tunisia, Yemen and Libya, Bahrain imposed martial law to try to crush the protests there last year.
Washington has urged Manama to hold a dialogue with the opposition to end the unrest and hold officials accountable for rights violations uncovered in an investigation led by international legal experts published in November.
But the United States values close ties with the ruling family, which allows Washington to run its Fifth Fleet operations out of Manama.
The fleet plays an important role in ensuring the free flow of oil in the Gulf at a time when Iran has threatened to block vital shipping lanes nearby if the United States increases pressure over Tehran's disputed nuclear programme.
(Writing by Andrew Hammond and Rania El Gamal; Additional reporting by Susan Cornwell; Editing by Robin Pomeroy and Pravin Char)