We are in it to win in Afghanistan, pledges Petraeus

During a ceremony at Nato headquarters, Gen Petraeus received two flags – one for the US and the other for Nato – marking his formal assumption of command.

He said it was important to demonstrate to the Afghan people and world that al-Qaida and its extremist allies will not be allowed to again establish sanctuaries in Afghanistan from which they could launch attacks on the US and other countries.

"We are in this to win," Gen Petraeus told a crowd of several hundred NATO and Afghan officials at the ceremony held just outside coalition headquarters. "We have arrived at a critical moment." Gen Petraeus succeeded General Stanley McChrystal, who was fired last month for intemperate remarks he and his aides made to Rolling Stone magazine about mostly civilian officials in President Barack Obama's administration.

"Upfront I also want to recognise the enormous contributions of my predecessor, Gen Stanley McChrystal," Gen Petraeus said.

He said the progress made reflected Gen McChrystal's "vision, energy and leadership". Gen Petraeus said the change in command did not signal a radical shift in Gen McChrystal's strategy of making the protection of the Afghan people the focus of the military mission.

He stressed the importance of avoiding civilian casualties, but said he would examine the civilian and military policies "to determine where refinements might be needed". That suggested he would review the rules under which Nato soldiers fight, including Gen McChrystal's curbs on the use of airpower and heavy weapons if civilians are at risk. Some troops complain such restraint puts their own lives in danger.

Gen Petraeus noted that June had been the deadliest month for the international force since the war began with 102 deaths – more than half Americans.