Bahrain Mirror- AFP: Bahrain on Sunday executed three men found guilty of killing three policemen, sparking violent protests and stoking tensions between the country's Shiite majority and its Sunni rulers.

The three Shiites faced the firing squad, six days after a court upheld their death sentences over a bomb attack in March 2014, the prosecutor's office said.

Bahrain, which has been ruled by the Al-Khalifa dynasty for more than two centuries, has a majority Shiite population which has long complained of marginalisation.

It has been rocked by sporadic unrest since March 2011 when security forces brutally crushed an Arab Spring-inspired uprising.

The executions triggered protests in Shiite villages.

Demonstrators blocked roads with burning tyres and police retaliated by firing tear gas, according to posts on social media.

Pictures shared online by activists showed relatives of those executed weeping.

Bahrain authorities do not permit international news agencies to cover events independently.

The executions came a day after demonstrations broke out following rumours they were going to be put to death.

The death sentences are the first in six years in the Gulf kingdom, according to London-based human rights group, Reprieve.

"It is nothing short of an outrage -- and a disgraceful breach of international law -- that Bahrain has gone ahead with these executions," Reprieve director Maya Foa said.

Reprieve said the executions went ahead "despite serious concerns that their convictions were based on evidence obtained under torture".

The European Union also condemned the sentences.

"This case is a serious drawback given that Bahrain had suspended executions for... (several) years, and concerns have been expressed about possible violations of the right to a fair process for the three convicted," an EU statement said.

- 'Black day' -

Sayed Ahmed Alwadaei, head of advocacy at the Bahrain Institute for Rights and Democracy, said: "This is a black day in Bahrain's history."

Scores of men and women took to the streets on Saturday after the families of the three were summoned to meet them in prison, a measure that usually precedes the implementation of death sentences, witnesses said.

"No, no to execution," the protesters chanted.

Later on Saturday, a policeman was wounded when his patrol came under fire in the Shiite village of Bani Jamra, said the interior ministry.

Authorities have said that the trio and fellow defendants belonged to the same clandestine group which has claimed several bomb attacks in Bahrain.

The high court on Monday upheld the death sentences against the trio convicted in a bomb attack in March 2014, which killed three policemen, including an officer from the United Arab Emirates.

The executed men have been named by activists as Sami Mushaima, 42, Ali al-Singace, 21, and Abbas al-Samea, 27.

Seven other defendants received life terms.

The Emirati officer was part of a Saudi-led Gulf force which rolled into Bahrain in March 2011 to help put down a month of Shiite-led protests.

Bahrain is a strategic ally of the United States and home to the US Navy's Fifth Fleet.

Iran's foreign ministry on Sunday criticised the Bahraini authorities for what it called an "inconsiderate action".

Lebanon's Shiite movement Hezbollah, backed by Iran, slammed the executions of the "innocent" men as a "crime committed by the regime against the Bahraini people".

"It is clear that this execution will destroy every chance for a political exit out of Bahrain's crisis, and leads the country into an unknown future, threatening stability in Bahrain and the whole region," it said.

Brian Dooley, director of Human Rights Defenders at the Washington-based Human Rights First, urged the United States to use its influence.

"Washington should warn its Gulf ally that this would be a reckless, frightening level of repression to pursue, likely to spark rage and further violence in an already volatile region," he said on Saturday.

And Britain's Foreign Secretary Boris Johnson said Manama had been made "fully aware" of his country's opposition to the death penalty.

Since the 2011 uprising, Bahrain has arrested and put on trial hundreds of Shiites and cracked down hard on the opposition, despite repeated appeals by international rights groups.