Pakistani Prime Minister Nawaz Sharif on Saturday described Pakistani Taliban's recent attacks as a serious setback for the ongoing peace talks between the militant group and the government. Sharif made comments two days after a deadly bomb attack on a police bus in the southern port city of Karachi killed 13 police officers and injured dozens of others. Taliban quickly claimed responsibility for the attack that created doubt about the success of the peace talks. The Taliban spokesman, Shahidullah Shahid, said the attack revenged Taliban members killed in Karachi and other cities in recent days by the police and paramilitary troops. The Taliban claimed responsibility for attacks in Karachi and Peshawar which prompted strong condemnation across Pakistan. "These attacks were sad and should have not occurred as we view such acts as a serious setback for the peace process," Sharif told Geo TV on board his special plane while returning from visit to Turkey. "The Taliban has sent an encouraging message to us through their intermediaries and we are happy that the process has started, " he said. He said the government had also held the Taliban accountable for killing innocent people in public places. "I am seriously concerned at the terror attacks during the ongoing peace dialogue," he said."It is my desire that no more innocent people loose their lives in terrorism." He said his government has started the dialogue with sincerity and formed a negotiating committee to take the process forward. He also hailed formation of a team of mediators by the Taliban but stressed that the bloodshed should be stopped. Sharif defended dialogue with the Taliban to seek political solution to the conflict. He said the political and military leadership had common ground on talks with the Taliban militants and the impression about differences were unfounded.