US General Stanley McChrystal, tasked with carrying out the new US strategy in the war against the Taliban, has formally assumed command of international troops in Afghanistan.

McChrystal, a former commander of special operations forces in Iraq and Afghanistan, was nominated in May after the United States sacked his predecessor and called for "new thinking" in the fight against the extremists.

The Taliban-led insurgency is now at its bloodiest level since 2001, when the hardliners were ousted in a US-led invasion, and troops face the urgent task of reining in the violence before presidential elections on August 20.

"The Afghan people are in the centre of our mission. In reality they are the mission. We must protect them from violence whatever its nature," McChrystal said at the headquarters of NATO''s International Security Assistance Force.

"2009 will be a critical year for Afghanistan and a critical year for our coalition, but while operating with care, we will not be timid," he said at the assumption of command ceremony attended by Afghan and Western officials.

McChrystal, who arrived in Afghanistan on Sunday, is expected to conduct a review of military strategy and make recommendations on any changes within two months of his arrival in Afghanistan, according to the Pentagon.