KABUL, (Reuters) – The nine-year war in Afghanistan  has reached a critical stage, U.S. General David Petraeus said  yesterday, 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  U.S. 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 U.S. and NATO troops on  Taliban strongholds in the country’s south.

“Nothing has been easy in Afgha-nistan,” 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 U.S. 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 U.S. Senate and the U.S. 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 U.S. 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 U.S.  Independence Day.