Suspected Sunni extremists opened fire on Shiite Muslim pilgrims traveling by bus through southwest Pakistan on Tuesday on their way to in Iran, killing 26 people, officials and survivors said.

Sunni militants with ideological and operational links to al-Qaida and the Taliban have carried out scores of bombings and shootings against Shiites in recent years, but this attack was especially bloody.

At least eight attackers in a pickup truck blocked the path of the bus as it traveled through Baluchistan province, and then forced the passengers off, said Khushhal Khan, the driver of the vehicle.

The passengers tried to run away, but the gunmen opened fire, killing 26 people and wounding six others, said Khan.

The attackers then drove off, leaving the dying and wounded where they lay. It was nearly an hour before rescue teams arrived, he said. There were around 40 people on the bus.

Local television footage showed rescue workers loading the dead and wounded into ambulances to take them to the main southwestern town of Quetta, about 35 miles (55 kilometers) to the north.

Lashkar-e-Jhangvi, one of the country's most ruthless Sunni militant groups, claimed responsibility in a telephone call to a local journalist in Quetta, but that claim could not be verified.

Vehicles carrying Shiite pilgrims are usually provided with protection as they travel through Mastung, but authorities weren't notified about this bus, said Saeed Umrani, a government official in Mastung. Iran and neighboring Iraq are home to many important Shiite shrines.

Pakistan is a majority Sunni Muslim state, with around 15 percent Shiite.

Most Sunnis and Shiites live together peacefully in Pakistan, though tensions have existed for decades. In the 1980s and 1990s, Pakistan became the scene of a proxy war between mostly Shiite Iran and Sunni Saudi Arabia, with both sides funneling money to sectarian groups that regularly targeted each other.

The level of sectarian violence has declined somewhat since then, but attacks continue. In recent years, Sunni attacks on Shiites have been far more common.

The groups have been energized by al-Qaida and the Taliban, which are also Sunni and share the belief that Shiites are infidels, and it is permissible to kill them.

Lashkar-e-Jhangvi is a Punjab-based group that has been implicated in scores of attacks on Shiites as well as attacks on government and security targets. In July, one of its alleged leaders, Malik Ishaq, was released from prison after being held for 14 year on charges, never proven, of killing Shiites.

Baluchistan is a lawless, poverty stricken province that borders Afghanistan and is home to scores of militants, as well as separatist rebels. Shiites there have been routinely attacked in recent years, and there have been few reported arrests or convictions.

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Associated Press writers Zarar Khan and Munir Ahmed contributed to this report.