Jamaat-ul-Ahrar, a Pakistani offshoot of the Taliban, has taken responsibility for killing more than 70 people in a public park on Sunday. At least 300 more were injured.
The group claimed to have specifically targeted Christians, who were celebrating Easter at the park with their children. A number of the casualties resulted from the people panicking and trampling each other.
The attack took place in the eastern city of Lahore, one of Pakistan's richest and most liberal cities. The regional government has declared three days of public mourning.
UN Secretary-General Ban Ki-moon has denounced the attack as "appalling" and called for those responsible to "be brought swiftly to justice."
Pakistan is a predominantly Muslim country. Christians are the second largest minority, following Hindus, though they only make up 1.6 percent of the population. Despite their small size, there have been a significant number of attacks on Christian targets in Pakistan in recent years. The worst to date was the 2013 bombing of a church in Peshawar that killed about 80 people.