A police special unit inspects the police patrol mini bus which was hit by explosions at a police checkpoint in the village of Dih, west of Manama. REUTERS/Hamad I Mohammed

Manama - An explosion rocked a bus carrying police in Bahrain on Friday, while security forces used tear gas in clashes with anti-government protesters on the third anniversary of an uprising in the small Gulf island nation.

Efforts to restart on-and-off reconciliation talks between the Shiite-dominated opposition and the Sunni monarchy and its allies have so far failed to bring an end to simmering unrest in the country, an American ally that hosts the U.S. Navy's 5th Fleet.

Activists frequently clash with police in the mainly Shiite villages just beyond the modern skyscrapers and shopping malls of the capital, Manama. Tensions intensified as the anniversary of the Arab Spring-inspired uprising approached, with government forces tightening security and activists blocking roads to Shiite communities with oil slicks and smoldering debris.

An explosion struck a minibus carrying police Friday evening in Dih, the Ministry of Interior said on its official Twitter feed. That community is a mainly Shiite village just west of the capital, Manama.

Photos released on the ministry's Twitter feed showed the side panels of the white bus torn from the chassis and twisted upward near the wheel wells.

A ministry official near the scene of the blast told reporters that three police officers were injured in the explosion. He insisted on anonymity because he was not authorized to speak publicly.

Anti-government factions have been increasingly using bombs targeting government forces, though they typically do not have the force of explosives used by insurgents in places such as Iraq or Syria. Authorities in late December announced the seizure of large amounts of explosives, automatic rifles and ammunition.

Earlier in the day, protesters were turned back by tear gas and stun grenades as they tried to make their way to the former site of Manama's Pearl Square, the focal point for the protest movement that started on February 14, 2011. The square was cleared by police raids and later razed in the early weeks of the unrest and is now sealed off by security forces.

Some of the youths marching Friday were seen carrying Bahraini flags, while others were masked and held unlit Molotov cocktails or metal rods. Police used tear gas to prevent them from approaching the former protest grounds.

Opposition groups dominated by the country's majority Shiites began protesting in 2011 to seek greater political rights from the country's rulers. More than 65 people have died in the unrest, but rights groups and others place the death toll higher.

Neighboring Sunni-ruled Gulf countries, led by Saudi Arabia, sent troops to Bahrain to help quell the uprising.

Many activists remain frustrated that too little has been done to meet their demands.

“After three years the government did not achieve anything, only besieging Pearl Square,” said Wajiha Ali, a 23-year-old mother of two. “I really want to live in a country that respects me and gives me my full rights. ... The government is not looking for long-term solutions, just security measures.”

On Thursday, the eve of the anniversary, 29 were arrested over “rioting and vandalism” in villages outside Manama, the Interior Ministry said.

Anti-government activists blocked roads to villages outside the capital with debris and smeared oil on the pavement to try to prevent security forces from entering. A car was burned by protesters and a school bus carrying children was attacked by “Molotov-throwing thugs,” the ministry alleged.

Repeated rounds of political talks have failed to significantly close the rifts between the two sides and the opposition is demanding amnesty for what they claim are more than 3 000 political prisoners held in Bahraini prisons.

Crown Prince Salman bin Hamad Al Khalifa met with top opposition leaders last month to once again revive the talks.

“The government is serious about dialogue and hope all others are also serious,” government spokeswoman Sameera Rajab told The Associated Press.

The main Shiite bloc al-Wefaq and other opposition groups see the negotiations as a positive step but have said their success depends on steps toward greater power sharing in the kingdom.

But many activists in the streets have taken a harder line, calling for the toppling of the government and at times clashing violently with police.

Al-Wefaq head Ali Salman and other opposition leaders have urged followers to rally to an anti-government demonstration scheduled to be held Saturday east of the capital.