It's believed mostly Christians were murdered in the suicide bombing by the Jamaat-ul-Ahrar faction, which happened at a funfair in Gulshan-e-Iqbal park in the city of Lahore on Easter Sunday evening.
Women and children are among the dead.
Christians were at the funfair as part of Easter Sunday celebrations, when a suicide bomber blew himself up just metres from the entrance.
Prime Minister David Cameron said Britain would be helping any foreign nationals in Pakistan, and tweeted his condolences along with the Foreign Secretary Phillip Hammond:
I'm shocked by the terrorist attack in Lahore. My thoughts are with the families and friends of the victims. We will do what we can to help.
— David Cameron (@David_Cameron) March 27, 2016
My thoughts are with victims of #LahoreBlast. UK utterly condemns senseless & shocking violence against innocent families.
— Philip Hammond (@PHammondMP) March 27, 2016
Shehbaz Sharif, the chief minister of Punjab province in which the city of Lahore is located, tweeted his condolences:
Heart bleeds at loss of precious human lives in Lahore. Words cannot describe agony we are in to see our children's blood spilled by cowards
— Shehbaz Sharif (@CMShehbaz) March 27, 2016
Wilson Chowdhry, Chairman of the British Pakistani Christian Association, told Premier:
"This recent attack is a clear targeting of Christians during their Easter celebrations.
"Families celebrating the resurrection of their Lord and Saviour have lost mothers and children as a consequence of this depraved violence.
"Pakistan is not safe for Christians as there is a genocide taking place there.
"Not a genocide that is state sponsored in it's entirety but a genocide nevertheless.
"Unless western governments wake up to this problem the death toll for Christians living there is set to rise exponentially."
The British Pakistani Association is helping to pay for the funerals of some of the victims, and has said hundreds of Christians are in need of support at this time.