Prime Minister David Cameron has promised British help for Pakistan after a terrorist bombing killed 65 people in a park in Lahore.
The device - believed to have been carried by a suicide bomber - was detonated near children's rides while families celebrated Easter.
A breakaway Pakistani faction of the Taliban claimed responsibility for the carnage and said it had deliberately targeted the Christian community.
More than 300 were injured in the attack on Sunday, many seriously.
Mr Cameron, who used his Easter message to urge Britons of all faiths to stand up for Christian values, said he was shocked by the attack.
"My thoughts are with the families and friends of the victims. We will do what we can to help," the PM posted on his Twitter feed.
Labour leader Jeremy Corbyn said: "My thoughts are with the victims and the family of the victims of the horrific attack in Lahore.
"Solidarity with the emergency services there."
Foreign Secretary Philip Hammond said British nationals were advised to avoid the area and monitor travel advice updates and local media.
"My thoughts are with the victims and their families," he said.
"The UK utterly condemns these senseless acts of violence.
"We will continue to provide support and assistance to the government of Pakistan as they work to defeat those who plan and perpetrate these acts of terror."