Pakistan's embattled Christian community suffered the most deadly attack in its history on Sunday when a pair of Taliban suicide bombers blew themselves up inside a church in the troubled city of Peshawar, killing 81 and wounding about 140.

The midday attack on the historic church was one of the most lethal aimed at civilians in Peshawar, a city that has been repeatedly struck by militant groups who control swaths of the nearby tribal areas.

Explosions ripped through the congregation of 500 people, including many women and children, as the service at All Saints church was coming to an end and worshippers were about to receive a free meal of rice in the courtyard outside.

Witnesses said the interior of the 130-year-old building was turned into a bloodbath, with severed limbs scattered around and the walls pockmarked with ball bearings used as shrapnel by the bombers.

"I saw myself in the air and then on the ground inside a huge fire of ball," said Sabir John, a worshipper who lost one of his arms in the blast.

An official from the provincial bomb squad said there was evidence of two suicide bombers, each carrying about 6kg of explosives. With a limited number of weekend staff, the city's main hospital was overwhelmed by casualties. There were fears that some would die of their injuries as they lay unattended on stretchers outside the emergency ward.

Dr Arshad Javed, chief executive of the Lady Reading hospital, said: "I have never seen such piles of human bodies. The exact number of the blast victims cannot be ascertained as yet."

Interior minister Chaudhry Nisar Ali Khan said on Sunday 78 confirmed dead included 34 women and seven children, Associated Press reported. Another 37 children were among the wounded, he said. A further three people died of their wounds overnight.

Distraught relatives were blocked from entering the hospital to look for family members by police. Some previous suicide bombings have been followed up with attacks on victims after they have been rushed to hospital.

Christians in Peshawar reacted with fury. Protesters outside the church chanted slogans attacking the provincial government for not providing security to worshippers. Some clashed with police, ripping off their uniforms and burning them in front of television cameras. Christians also came out to protest in cities around the country.

The Jundullah wing of the Pakistani Taliban claimed responsibility. A spokesman said: "They are the enemies of Islam, therefore we target them. We will continue our attacks on non-Muslims on Pakistani land."

The highly unusual attack on Christian worshippers was reminiscent of a series of brutal bombings against large gatherings of Shias, a minority Muslim sect reviled as heretics by some militant groups. Until now Pakistan's Christian minority, thought to be about 2% of the near 200 million population, have been spared such attacks, though five people were killed by a grenade attack in 2002 on a church in Islamabad frequented by foreigners.

Christians, who tend to be among the poorest sections of society, have suffered prejudice and sporadic bouts of mob violence and church burnings, usually triggered by accusations of anti-Islam blasphemy.

Sunday's attack is likely to be seen as yet another sign of the growing threat from Pakistan's fast-evolving network of militant groups, which include sectarian terrorists, anti-India groups and a homegrown strain of the Taliban influenced by al-Qaida ideology. It could further undermine hopes of a negotiated peace settlement with militants.

An agreement struck earlier in September by leading political parties gave the green light to the government to hold talks with militants, but it did not lead to any reduction in attacks. Counter-terror analysts believe the peace initiative is doomed to fail because the violent fundamentalists ravaging the country reject Pakistan's government and constitution as un-Islamic.

On Sunday three days of mourning were announced as politicians and religious leaders condemned the attack.

"Terrorists have no religion and targeting innocent people is against the teachings of Islam and all religions," said the prime minister, Nawaz Sharif, in a statement. "Cruel acts of terrorism reflect the brutality and inhumane mindset of the terrorists."

Imran Khan, the politician whose party leads the provincial government in Peshawar, rushed to the city from the capital, Islamabad.

Talking to journalists outside the hospital he said the attack was a deliberate scheme to scupper peace talks. "Isn't it strange that whenever peace talks are pursued, these attacks take place, and I want to point out that there was also a drone strike today," he said in reference to a strike by an unmanned US aircraft that killed six suspected militants in North Waziristan on Sunday. Khan has long blamed the CIA's drone campaign as the root cause of Pakistan's current unrest, a position decried by his critics who say militancy and extremism long pre-date drones and the US-led intervention in Afghanistan.