WASHINGTON Amid heightening Islamabad-Washington tensions, Chairman of the Joint Chiefs of Staff Admiral Mike Mullen told a US Senate committee Thursday that Pakistans intelligence agency aided the insurgents who attacked the American Embassy in Kabul last week. In comments that were the first to directly link the Inter-Services Intelligence (ISI) with an assault on the United States, Mullen went further than any other American official in blaming the ISI for undermining the American military effort in Afghanistan. The attack on the American embassy, and the alleged ISI support for the Haqqani network which also forms one of the most lethal parts of the insurgency attacking American forces in Afghanistan is the latest point of tension setoff by US unilateral raid that killed Osama bin Laden. With ISI support, Haqqani operatives planned and conducted that truck bomb attack, as well as the assault on our embassy, Admiral Mullen told members of the Senate Armed Services Committee. We also have credible evidence that they were behind the June 28 attack at the Inter-Continental Hotel in Kabul and a host of other smaller but effective operations. The Haqqani network acts as a veritable arm of Pakistans Inter-Services Intelligence Agency, he asserted. The truck bomb attack that Admiral Mullen referred to occurred at a Nato outpost south of Kabul on Sept 10, when a cargo vehicle packed with explosives killed at least five people and wounded 77 coalition troops. The injury toll was one of the worst for foreign forces in a single episode in the 10-year-old war. Admiral Mullen testified alongside Defence Secretary Leon Panetta, who told the committee that the attack on the embassy and the assassination this week of Burhanuddin Rabbani, the leader of Afghanistans High Peace Council and a former Afghan president, were a sign of weakness in the insurgency. He cast the attacks as signs that the Taliban had shifted to high-profile targets in an effort to disrupt the progress the American military has made. Over all, we judge this change in tactics to be a result of a shift in momentum in our favour, Panetta said. No one has yet claimed responsibility for the attack on Rabbani. Despite his optimistic remarks about American progress, Panetta said the American military had a difficult job ahead and had to do better in preventing the insurgents from attacking. While overall violence in Afghanistan is trending down and down substantially in areas where we concentrated the surge we must be more effective in stopping these attacks and limiting the ability of insurgents to create perceptions of decreasing security, Panetta said. The hearing, called by the panel to review American military policy in Iraq and Afghanistan, was the first for Panetta as defence secretary. We must not attribute more weight to these attacks than they deserve, Admiral Mullen said. They are serious and significant, but they do not represent a sea change in the odds of military success. Admiral Mullen voiced a stern warning to Pakistan, who he said was undermining its own interests as well as the American interest in fighting terror networks in the region. In choosing to use violent extremism as an instrument of policy, the government of Pakistan, and most especially the Pakistani army and ISI, jeopardises not only the prospect of our strategic partnership but Pakistans opportunity to be a respected nation with legitimate regional influence, he said. They may believe that by using these proxies, they are hedging their bets or redressing what they feel is an imbalance in regional power. But in reality, they have already lost that bet. By exporting violence, theyve eroded their internal security and their position in the region. They have undermined their international credibility and threatened their economic well-being. But he said he did not believe he had wasted his time by pouring so much effort into improving ties with Pakistans government. Ive done this because I believe that a flawed and difficult relationship is better than no relationship at all, he said. Some may argue Ive wasted my time, that Pakistan is no closer to us than before, and may now have drifted even further away. I disagree. Military cooperation again is warming. Mullen said more than a dozen meetings with Army Chief General Ashfaq Parvez Kayani were crucial despite Islamabads refusal to meet Washingtons demands. Indeed, I think we would be in a far tougher situation today, in the wake of the frostiness which fell over us after the bin Laden raid, were it not for the groundwork General Kayani and I had laid were it not for the fact that we could at least have a conversation about the way ahead, however difficult that conversation might be. Agencies add:The admirals tough language follows a series of stern warnings from top US officials on Pakistans failure to crack down on the Haqqani network, raising the possibility of unilateral US action. If they keep killing our troops that would not be something we would just sit idly by and watch, Mullen said of the Haqqani insurgents. Leon Panetta expressed frustration over Haqqani 'sanctuaries in Pakistan and renewed a vow that the United States would safeguard its troops. When asked by Senator Carl Levin to elaborate, Panetta declined to say what steps the government might take - amid speculation the United States might expand drone strikes to a wider area or even stage an operation similar to the Bin Laden raid. But he said the US had made clear that it would do whatever is necessary to protect its troops. You know I havent spelled that out for them, but I would be very surprised if they were surprised by what we did to fulfil that commitment, he said. Panetta said Pakistan needed to take action not only on the Haqqani network but also to cooperate on tracking down prominent extremists identified by Washington and to bolster campaign against militants inside its borders. The CIA already carries out drone bombing raids on al-Qaeda and other militants in Pakistans northwest tribal areas, which US officials do not explicitly acknowledge. Washingtons relations have grown increasingly strained with Pakistan, which was angered and embarrassed by a US raid on May 2 that killed al Qaeda chief Osama bin Laden in Abbottabad. On the other hand, a key US Senate committee voted Wednesday to tie aid to Pakistan to greater cooperation from Islamabad in fighting the Haqqani network and other militant groups. The Senate Appropriations Committees action, which requires approval from the full Senate and the House of Representatives, comes as Washington has escalated calls for action against the group. The panel did not specify a level of economic aid for Pakistan, a rare step that left it to President Barack Obama to decide, but provided $1 billion for a fund meant to help the countrys military battle insurgents. The amount was $100 million below Obamas request, the committee said in a statement. If the administration wants to provide zero, thatd be OK with us, said Republican Senator Mark Kirk, one of the more vocal critics of Pakistan on the panel. The committee voted to make this aid, as well as any economic aid that is provided, conditional on Pakistans cooperating with Washington against several militant groups. In addition to the Haqqani network, these groups include al-Qaeda, Quetta Shura and Lashkar-e-Taiba. Pakistan gets US military aid via the Pentagon budget. But Washington is already withholding $800 million of that aid this year as ties have come under mounting strain. Many lawmakers have been calling for aid to Pakistan to be reduced since US special forces found and killed al Qaeda leader Osama bin laden in a Pakistan military town on May 2.