Taliban militants have attacked worshippers at a Shia mosque in the Pakistani city of Peshawar with guns and grenades, killing at least 20.
Police killed one of the militants in a gunfight around the mosque, in the wealthy Hayatabad district.
Another of the militants blew himself up with a suicide vest, and a third was arrested, police said.
Two weeks ago, another attack on a Shia mosque in Sindh province's Shikarpur district left more than 60 people dead.
Sunni militants linked to the Taliban said they had carried out the Shikarpur attack, which was the deadliest in years.
Pakistani Prime Minister Nawaz Sharif expressed his grief for the loss of life and said that the government remained committed to "eradicating the menace of terrorism".
Over the past decade, Pakistan has experienced an increasing number of sectarian attacks.
Most are carried out by hardline Sunni Muslim groups against Shias, who comprise about 20% of the population.
In Peshawar, TV footage on Friday showed people running from the scene, some carrying wounded people on their shoulders.
Police chief Mian Saeed said the militants stormed the mosque wearing suicide vests. However, only one attacker managed to detonate his.
The other two reportedly threw grenades and shot at worshippers gathered for Friday prayers.
The head of the provincial police, Nasir Durrani, said that worshipers prevented one of the attackers from detonating his vest.
"People here showed great courage. They grabbed one of the attackers from his neck, and he couldn't detonate [his explosives], and he was shot and killed."
The Pakistani Taliban said their fighters had carried out the attack, claiming that it was in revenge for the execution of one of their members.
The Taliban have carried out a number of atrocities in Peshawar, including an attack on a school in December in which 150 people were killed.
The government reacted to the school attack by ramping up security, forming an anti-Taliban combat group and allowing teachers to carry guns.