Three other activists, who were also on trial, were sentenced to life in prison after they were convicted of playing a role in the policemen's deaths.

The verdicts, which can be appealed, were the first related to Bahrain's uprising.

Bahraini human rights groups blasted the verdict and said the trial, conducted in secrecy, had no legal credibility and was politically motivated.

"This verdict is a message from the government, determined to stop the democracy movement," said Nabeel Rajab, head of the Bahrain Center for Human Rights. "It's a warning saying 'this is how we will treat you if you continue to demand your rights'."

Faced with unprecedented political unrest, Bahrain's king declared martial law and invited troops from Gulf neighbors to help quell the unrest after weeks of street marches and bloody clashes in the capital Manama. At least 30 people have died since Feb. 15, when the anti-government protests erupted. Four opposition supporters have also died in police custody.

The seven opposition supporters sentenced Thursday were tried behind closed doors on charges of premeditated murder of government employees. In an earlier hearing this week, Bahrain state media said the military prosecutor presented evidence that showed the defendants killed the policemen intentionally by running them over with a car.

Their lawyers denied the charges.

International rights groups have expressed deep concern over the verdict that followed a trial of civilians in a military court, set up under emergency laws.

"This is very worrisome by the international standards for fair trials," said Malcolm Smart, a Middle East and North Africa director with Amnesty International.

The president of the European Parliament, Jerzy Buzek, denounced the death sentences and called the closed-door trial "deplorable." Foreign media was barred from the courtroom, but selected representatives from state-aligned media were allowed.

Family members of the defendants also attended the trial. A relative of one of the defendants sentenced to death, said there were no emotional outbursts in the courtroom when the verdicts were read.