A suicide bomber blew himself up among a crowd at a public park in eastern Pakistan on Sunday, killing 65 people and wounding over 315, officials said.
Most of the dead and injured were women and children, said Mohamed Usman, chief administrator in the city of Lahore, where the attack took place.
The death toll may go up as some of the injured people are in a critical condition, Khawaja Salman Rafique, health adviser of the central Punjab province, said.
The bomber targeted the children’s play area as people were leaving the park in the evening, police official Haider Ashraf said.
The attack took place as Christians in Pakistan celebrated the festival of Easter, but it was not clear if the members of the minority community were the target, Ashraf said.
Indian Prime Minister Naredra Modi called his Pakistani counterpart Nawaz Sharif to codemn the attack.
The US described the terrorist attack as "cowardly" and pledged to work with Pakistan and other partners in the region to "root out the scourge of terrorism," White House spokesman Ned Price said.
No group has so far claimed responsibility for the deadliest attack to hit Pakistan in several months.
Pakistani military launched an offensive in June 2014 against Islamist militants linked with al-Qaeda in the country’s north-western tribal regions on the Afghan border. Since then, the number of attacks has decreased, although sporadic violence has persisted.
More than 3,500 militants have so far been killed in the year-and-a-half campaign, according to the military.