year war in Afghanistan has reached a critical stage, US General David Petraeus said on Sunday, as he formally took command of the 150,000-strong NATO-led force fighting a growing Taliban insurgency. “We are engaged in a tough fight. After years of war we have arrived at a critical moment,” Petraeus told guests at a change-of-command ceremony at the NATO-led International Security Assistance Force (ISAF) headquarters in Kabul. “We all recognise the threat that the Taliban, al Qaeda and the other associated syndicate of extremists pose to this country, this region and to the world,” he said. “We are in this to win.” Petraeus was last week appointed to lead all foreign forces in Afghanistan after his predecessor, General Stanley McChrystal, was dismissed for insulting remarks he and aides made about the U.S. administration in a magazine interview. The shift comes as the Taliban are at their strongest since being overthrown in 2001, and with ISAF casualties mounting daily. Suicide bombers and insurgent fighters also attacked a US aid contractor's office in northern Kunduz last week, killing five people and wounding dozens more. Petraeus, wearing camouflage fatigues and speaking near a marble column dedicated to ISAF troops killed in the Afghan campaign, told senior commanders and several Afghan ministers his appointment signalled a change in command, not strategy. Despite last month being the bloodiest yet for international troops, he said gains were being made in the increasingly difficult war and a pushback by insurgents had been expected ahead of an offensive by US and NATO troops on Taliban strongholds in the country's south. “Nothing has been easy in Afghanistan,” he said. “However, we can all take heart from the progress that has been made on the security front and beyond.” New Afghan interior minister Besmillah Mohammadi said after watching Petraeus take command that US troops and Afghan police had killed 63 Taliban fighters during a two-day sweep in the restive southern Helmand province. Petraeus landed in Kabul on Friday after his appointment was confirmed by the US Senate and the US House of Representatives approved $33 billion in funding for a troop surge he hopes will turn the tide of the war. The surge will bring to 150,000 the number of foreign troops in Afghanistan just as a new strategy takes root. It entails tackling the Taliban in the south while relying on the government to improve local governance and development. “We must demonstrate to the Afghan people and to the world that Al-Qaeda and its network of extremist allies will not be allowed to once again establish sanctuaries in Afghanistan,” Petraeus said, calling again for unity between the government and international forces. Petraeus accepted ISAF and US command flags on a small lawn and under tight security, watched over by rooftop snipers and with several top commanders arriving in a convoy of helicopters for a low-key ceremony coinciding with US Independence Day.