At least 19 people were killed on Friday in the Pakistani city of Peshawar in a series of explosions targeting a Shi'ite mosque, in the latest sectarian attack to hit the South Asian nation.
Radical Sunni Islamist groups often target mosques frequented by minority Shi'ites, whom they see as infidels.
Police said a group of armed men broke into the mosque, where people were attending Friday prayers, and opened fire, following which three explosions were heard inside the building.
"Police have been called and an operation has started against the terrorists," said Mian Saeed, police chief of the northwestern city.
The Pakistani Taliban, who are fighting against the state to set up a hardline Sunni theocracy in Pakistan, claimed responsibility.
Peshawar's Hayatabad Medical Complex said at least 19 people had been killed.
A witness, Shahid Hussain, told Reuters the worshipers had just finished prayers when five or six men wearing military uniforms broke into the mosque and started shooting.
"We had no idea what was going on. One of the attackers then blew himself up and then there was huge smoke and dust all around," he said.
The attack came as Pakistan tries to adopt new measures to tackle Islamist militants following a massacre of 134 children on Dec. 16 at an army-run school in Peshawar.
The government has pledged to crack down on all militant groups, and has reintroduced the death penalty, set up military courts to speed convictions and widened its military campaign in northwestern areas on the Afghan border where militants find refuge.
Yet Pakistan's religious minorities, among them Ahmadis, Christians and Hindus, say the government is doing little to alleviate their daily struggle against humiliation, discrimination and violence.
Last month, dozens of people were killed in a similar attack on a Shi'ite mosque in the southern town of Shikarpur.
REUTERS