Archbishop Joseph Coutts of Karachi also demanded that the Pakistani government take immediate steps to apprehend those responsible for the attack and to take measures to protect the worship sites of all religious minorities in Pakistan.
"We condemn this act in strongest terms," Archbishop Coutts said in a Sept. 22 statement.
The death toll in the bombing had reached 85 by early Sept. 23. Authorities expected it to increase because many of the 150 who were injured were in critical condition.
Police said two suicide bombers, each wearing more than 13 pounds of explosives, detonated themselves following a Sunday service as 600 members of the Protestant church gathered on the church lawn for food distribution.
Jundallah, a group linked to the Pakistani Taliban, claimed responsibility for the attack, saying it was in response to U.S. drone strikes, the latest of which Sept. 22 reportedly killed seven people in the tribal area of North Waziristan.
"Until and unless the drone strikes are stopped, we will continue to strike wherever we find an opportunity against non-Muslims," said a Jundallah spokesman.
"This tragedy of unprecedented scale saddens us all," said a Sept. 23 statement from Peter Jacob, head of the Catholic bishops' National Commission for Justice and Peace in Pakistan.
"Rather than an emotional outburst/reaction we need to strengthen our efforts and initiatives for a long-term response," he said. "For us it is a foregone conclusion that peace is the way to change."
But already enraged Christians took to the streets in cities across the country to protest the attack, with many condemning both the government and the militants. One Lahore demonstration demanded the resignation of the provincial official responsible for providing security to its religious minorities.
The Khyber Pakhtunkhwa government announced compensation of 500,000 rupees ($4,750) for the victims' families and three days of mourning in the state.
"We condemn the horrible act," said Victor Azariah, general secretary of the Lahore-based National Council of Churches in Pakistan, which encompasses all the major non-Catholic Christian churches. "The government should not take it lying down. It should crush the terrorists, otherwise they will continue to do the same. The nation has been suffering from such dastardly actions for long."
Azariah expressed relief that media, human rights and prominent Muslim groups had joined the chorus of protest against the deadly suicide blasts.
Pakistani Prime Minister Muhammad Nawaz Sharif strongly condemned the bomb blasts, expressing sorrow and shock over the loss of life.
"Terrorists have no religion, and targeting innocent people is against the teachings of Islam and all religions," he said.