PESHAWAR: Sectarian gunmen ambushed a bus on Tuesday, killing 18 Shia Muslims in a usually peaceful region of northern Pakistan that neighbours the former Taliban stronghold of Swat, officials said.

The bus was stopped, before passengers were ordered off and shot in the mountainous district of Kohistan as it travelled from Rawalpindi to the northern city of Gilgit.

“Armed men hiding on both sides of the road attacked the bus,” local police chief Mohammad Ilyas said.

“Eighteen people have died and eight wounded,” he added. The ambush happened near the town of Harban, 130 miles (208 kilometres) north of the capital Islamabad.

Survivors said seven or eight gunmen stopped the bus, forced the passengers to get off and then opened fire, regional administration chief Khalid Omarzai told AFP by telephone, confirming the casualty numbers.

“It appears to be a sectarian attack,” local MP Abdul Sattar Khan said.

“Its a remote area. We are getting reports that the gunmen forced people to get off the bus. They checked their papers and shot them dead,” he told AFP.

The victims were Shia Muslims, he said. “It could be the outcome of the murder of two Sunni Muslims a few days ago in Gilgit. The people of the area had vowed they would take revenge,” Khan added.

Authorities were slow to confirm the motive and insisted militants are not active in the area.

Kohistan borders the Swat valley, where Pakistan in 2009 managed to put down a two-year Taliban insurgency.

Omarzai told AFP that he could not immediately confirm whether it was a sectarian attack, saying that the police were investigating.

President Asif Ali Zardari and Prime Minister Yousuf Raza Gilani had strongly condemned the Kohistan incident.

The two leaders directed the concerned authorities to ensure best medical treatment for the injured.

Gilani said such incidents  could not deter the government's resolve to fight the menace.

While the president said the culprits of such heinous crime would not be spared