There is evidence linking the Pakistani government with the Taliban-allied Haqqani network of militants, the US ambassador in Islamabad said, blaming the group for last week's siege in Kabul. In blunt comments broadcast by state-run Radio Pakistan on Saturday, ambassador Cameron Munter said: "Let me tell you that the attack that took place in Kabul a few days ago that was the work of the Haqqani network... "There is evidence linking the Haqqani network to the Pakistan government. This is something that must stop," Munter said. His remarks follow a warning by US Defense Secretary Leon Panetta, who said after the Kabul attack -- in which rebels fired rockets at the US embassy and NATO headquarters, leaving 15 dead -- that the US would retaliate against Pakistan-based insurgents. The US has long urged Pakistan to take action against the Haqqani network and suspected the group had support within the Islamabad administration. But the public comments are a mark of strained ties between the fragile anti-terror allies, with relations fractious since the US raid on Pakistani soil that killed Al-Qaeda leader Osama bin Laden in May. Asked to provide evidence of the link with the Pakistani government, Munter said only "we believe that to be the case". Acknowledging that the past year had been "tough", he urged joint action against terrorism and said that the United States and Pakistan were "fundamentally on the same side". The Haqqani network is thought to have been behind a number of attacks in Afghanistan, where NATO plans a gradual withdrawal of troops after a gruelling ten-year war. Militants frequently cross the porous Afghan-Pakistani border. "The key here is that this is going to take a real effort to work together, to identify who the enemy is," Munter said. "Time and again we've urged the Pakistanis to exercise their influence over these kinds of attacks from the Haqqanis and we've made very little progress in that area," Defense Secretary Panetta said Wednesday, a day after the Kabul siege. "I'm not going to talk about how we're going to respond. I'll just let you know that we're not going to allow these kinds of attacks to go on," he said. Pakistan's foreign ministry condemned those remarks as "out of line", saying that "terrorism and militancy is a complex issue". The top US and Pakistani military leaders are to meet in coming days on the sidelines of a NATO conference in Spain in the hope of mending strained ties. The 19-hour Taliban assault on Kabul turned the city's most heavily secured district into a battle zone, with six foreign troops wounded in the attack. NATO's force in Afghanistan said Thursday it had captured two suspects over the siege, one of them a member of the Haqqani network and the other a Taliban militant who had also planned vehicle-bomb attacks. Before the Kabul attack, the US military blamed Haqqani militants for a truck bombing on September 10 against a NATO base in Wardak province, which wounded 77 American troops. Thousands of Pakistani troops have been killed fighting insurgents, but Islamabad has focused mainly on combatting the Pakistani Taliban. US officials have accused Pakistani intelligence of playing a double game with extremists, including the Afghan Taliban and the Haqqani network, in order to exert influence in Afghanistan and offset the might of arch-rival India. Jalaluddin Haqqani, founder of the network, and his son Sirajuddin, who now runs the group, have both been designated "global terrorists" by Washington.