A pair of suicide bombers blew themselves up outside a church in the Pakistani city of Peshawar, killing 40 people after Sunday mass.
Police said the death toll included at least four children, two policemen and six women and was likely to rise.
Reuters reports 70 people were wounded.
More than 600 parishioners were inside the church for the service.
A senior police officer said that after the service ended, people started to come out and a suicide bomber rushed towards them.
Christians, Shi'ite Muslims and Ahmadis are victims of a rising tide of deadly attacks in Pakistan.
Sectarian violence and attacks on security forces have been on the rise in past months, a major challenge for the government of Nawaz Sharif.
The violence has also undermined his call to engage militants in peace talks.
In 2009, 40 houses and a church were set ablaze by a mob of 1000 Muslims in the town of Gojra in Punjab province.
At least seven Christians were burnt to death.
The attacks were triggered by reports of the desecration of the Koran.
