At least 20 people have been killed in a powerful bomb blast at aShia mosque in southern Pakistan, officials say.
Police said that at least 50 people were wounded in the attack after Friday prayers in the Shikarpur district of Sindh province.
The death toll is expected to rise as many of the wounded are in a critical condition.
Local media reports suggest that the blast could have been a suicide attack, but police are investigating.
It is not yet clear who carried out the attack but Sunni militant groups have targeted the Shia minority in the past.
A number of people were trapped after the roof of the mosque collapsed due to the force of the explosion, local media said.
Senior police official Abdul Qudoos Kalwar told the Associated Press news agency that four children were among the dead.
Pakistan Prime Minister Nawaz Sharif has condemned the incident and ordered an immediate inquiry.
The attack came as Mr Sharif visited the city of Karachi, the capital of Sindh province.
The BBC's M Ilyas Khan in Islamabad says that attacks on Shia targets have been fairly common in Karachi, on the coast, but are relatively new in the interior of Sindh province, where the influence of a more tolerant Sufi Islamic tradition is more widespread.
Our reporter says that Friday's incident is reportedly the fifth attack of a sectarian nature in the province's interior since 2010.