"Such incidents do not augur well for negotiations," he told reporters in London on his way to New York, where he is scheduled to attend the 68th session of the UN General Assembly.
"Unfortunately, because of this, the government is unable to move forward on what it had envisaged, on what it had wished for," The Express Tribune quoted him as saying.
At the same time, he instructed the authorities concerned to devise a new security plan for the worship places of the country's religious minorities.
"We had proposed peace talks with the Taliban in good faith, and with the consent of all political parties... but unfortunately, because of this (attack) the government is unable to move forward on what it had envisaged, on what it had wished for," he said.
He said All Parties Conference was called with sincere intentions and "all the decisions made there were based on sincerity and the whole nation was represented in the decisions that were made."
Nawaz defended the APC's decision to speak to the militants but looked frustrated at the total disregard shown by them to his offer, the report said.
He said that the killing of innocent Christians had plunged the whole nation into grief.
"It's a national tragedy. No sane person can condone such barbarism. Everyone, no matter what his religion or creed is, will feel sad over this. This is the work of the enemies of Pakistan," he was quoted as saying.
The prime minister said those who carried out the gruesome attack had violated the tenets of Islam.
"Terrorists have no religion... targeting innocent people is against the teachings of Islam and all religions," he said.
"Such cruel acts of terrorism reflect the brutality and inhumane mindset of the terrorists," he added.
Terming those responsible for the attack 'enemies of Pakistan', the premier said the government will take action against extremist elements in the country after consulting all sides on the matter.
The News daily said Sharif has conceded that the continuing attacks on Pakistan’s interests by terrorists have dealt a blow to the sincere efforts of the government.
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