KABUL (AFP) - US General David Petraeus appealed Saturday for a united effort to end almost nine years of war against the Taliban as he made his public debut as the commander of NATO forces in Afghanistan. The four-star general, who arrived in the Afghan capital on Friday, faces a tough task to bring peace and secure a face-saving exit for allied troops fighting an increasingly deadly insurgency. This is an effort in which we must achieve unity of effort and common purpose. Civilian and military, Afghan and international, we are part of one team with one mission, Petraeus said at the US embassy in Kabul. On this important endeavour, cooperation is not optional, Petraeus added. Petraeus, who took over as commander of the 140,000 US and NATO troops in Afghanistan after the sacking of US General Stanley McChrystal, has said the war is likely to get tougher before significant improvements are seen. This is a tough mission, there is nothing easy about it. But working together we can achieve progress and we can achieve our mutual objective, he told some 1,700 invited guests at a Fourth of July reception. Petraeus was due to formally assume his commander role on Sunday in a ceremony at NATOs ISAF headquarters in central Kabul. But he has already started on the job, leading Saturdays morning briefing of regional commanders across the country, said ISAF public affairs officer US Air Force Lieutenant Colonel Tadd Sholtis. General Petraeus received his first operational update from the ISAF staff during the commands daily morning stand-up briefing, Sholtis said. He was actively engaged in asking questions and providing guidance to headquarters personnel and subordinate commands connected to the meeting, he said. Analysts have urged Petraeus to make immediate adjustments to turn around rapidly a war seen as bogged down to the Talibans advantage. Petraeus must change the fundamental strategy of the war against the Taliban, said parliamentarian Ahmad Behzad. A change in the leadership of foreign forces can only be effective if we see more serious steps taken against terrorists, he told AFP.