Police in Islamabad were on high alert Sunday after a deadly suicide blast, as the prime minister insisted a spike in attacks would not deter an anti-Taliban offensive. Two policemen were killed late Saturday when a suicide bomber walked up to a police emergency helpline centre in an Islamabad residential district where many government officials live and detonated explosives strapped to his body. The nighttime assault came after a suicide blast killed 38 people during Friday prayers at a mosque in Upper Dir, near three northwest districts hit by a six-week military offensive against Taliban fighters. "Islamabad police are on high alert. We have taken tough security measures after the bombing on Saturday," a senior police official said, asking not to be named as he was not authorised to speak to the media. "They are conducting surprise checks of vehicles. A combing operation is underway to trace the culprits. We are hopeful the accused would be arrested over the next few days." No group has yet claimed responsibility for the attack. Saturday's bombing is the latest in a series of attacks on civilian and security targets -- attacks widely seen as retribution by Islamist extremists for Pakistan's blistering air and ground offensive. Since the offensive began in late April more than a dozen bomb blasts have killed over 100 people, with Peshawar, the main city in the northwest, Pakistan's cultural capital Lahore and now Islamabad all hit. Prime Minister Yousuf Raza Gilani condemned the Islamabad attack, calling it a "cowardly act of terrorism," a statement from his office said late Saturday. "The prime minister reiterated his governments resolve to stamp out the menace of militancy and terrorism, adding that such incidents will not deter the governments commitment to eliminate this scourge from the country," it added. Pakistan launched its northwest push after the Taliban advanced to within 100 kilometres (60 miles) of Islamabad in early April, violating a deal to put the region's three million people under sharia law in exchange for peace. Bomb attacks across Pakistan blamed on Islamist extremists have killed more than 1,900 people in the nuclear-armed US ally in the past two years.