At least ten people have been killed in the southwestern Pakistani city of Quetta, after a bomb targeted a bus carrying Shia pilgrims, officials say.
The bus was attacked with a bomb and gunfire on Thursday, and was carrying around 40 passengers from Iran to Quetta, the capital of the Balochistan province, said senior local police officer Hamid Shakeel.
"It was a remote controlled blast. The bomb was planted in a car and exploded as the bus passed by it," he said, confirming that among the dead were two escorting police officers and two female pilgrims.
In addition to those killed, 25 people were wounded, said Mohammed Jafar, a doctor at the main hospital in Quetta.
Footage from local television news networks showed rescue workers using a crane to lift the blackened remains of the bus out of a ditch where it fell during the attack.
Shakeel said the engine of the car used in the attack was found about 50 feet away from the site of the explosion.
Manzoor Ahmed, a bomb disposal squad official, said the improvised explosive device weighed more than 30kg.
The attack comes a day after a bomb planted underneath a tea stall at a railway station in southwestern Pakistan killed seven people, including a child. More than a dozen others were wounded in that attack.
Balochistan has increasingly become the site of sectarian violence between the country's majority Sunni Muslims and the minority Shias, who account for about a fifth of the country's more than 170 million population.
Most Shias and Sunnis live peacefully together, but extremists on both sides have targeted each other over the past three decades.
Balochistan is also the site of a regional insurgency waged by separatists who are demanding political autonomy and a greater share of the wealth generated from the province's natural resources.
This month, UN human rights chief Navi Pillay voiced concern about "very grave" rights violations during Pakistani military operations.
The province is one of the most deprived regions of Pakistan, despite its natural resource wealth. Human rights activists say the military has been carrying out mass arrests and extra-judicial executions as part of operations to control the insurgency.
Around 5,000 people have been killed in outbreaks of sectarian violence between Sunni and Shia extremist groups in Pakistan since the late 1980s.