Two suicide bombers blew themselves up while worshippers were leaving the city's historic All Saints church after attending Sunday Mass.

A hospital spokesperson said that at least 120 people had been wounded in the attack.

Jundullah said it was in retaliation for US drone strikes in Pakistan's tribal northwest.

The attack occurred as hundreds of worshippers were coming out of the church in the city's Kohati Gate district after services to get a free meal of rice offered on the front lawn, said a top government administrator, Sahibzada Anees.

"There were blasts and there was hell for all of us," said Nazir John, who was at the church with at least 400 other worshippers. "When I got my senses back, I found nothing but smoke, dust, blood and screaming people. I saw severed body parts and blood all around."

The white walls of the church, which first opened in the late 1800s, were pockmarked with holes caused by ball bearings or other metal objects contained in the bombs to cause maximum damage.

Pakistan's Prime Minister Nawaz Sharif condemned the "cruel" attack, saying it violated the tenets of Islam.

RA/SHI