US Secretary of State Condoleezza Rice acknowledged "difficult going" fighting a resurgent Taliban in Afghanistan, but insisted that the world cannot afford to pull out now.
US Secretary of State Condoleezza Rice
"We owe it to the people of Afghanistan to help them finish the job," Ms Rice said as she thanked Canada for its role as a leader of Nato forces in the country.
Canada's combat role is unpopular at home, as is the US-led war in Iraq. Afghanistan is struggling with the deadliest militant violence since US-led forces toppled the hard-line Taliban regime five years ago.
The United States blamed the Taliban for incubating al-Qaeda as a terrorist force and for harbouring Osama bin Laden after the September 11, 2001 terror attacks.
Canada has 2,200 troops in Afghanistan and has lost at least 20 soldiers there.
Opponents of the Afghanistan mission suggested Ms Rice's visit to Canada was an attempt to persuade Canada to commit more forces.
Tony Blair today stressed the "fundamental importance" of the war in Afghanistan for Britain's security — as he called on other Nato countries to take their share of the burden there.
The Prime Minister paid tribute to the "bravery and commitment" of the 5,000 UK troops in the country but stressed: "It is important that the whole of Nato regards this as their responsibility."
Nato's Secretary General Jaap de Hoop Scheffer has called for more forces to be sent to help the fight against the Taliban and al Qaida but has had few offers of extra troops from alliance members.
Mr Blair, speaking to reporters in 10 Downing Street after talks with Chinese premier Wen Jiabo, said: "Nato is looking at what further requirements there are and Nato and Nato countries have got a duty to respond to that.
The deadliest fighting since the fall of the Taliban government has killed more than 500 people, mostly militants, since mid-May and confirmed fears of a Taliban military resurgence in southern Afghanistan, where Nato took command from a US-led coalition on August 1st.
Britain, Canada and the Netherlands have taken lead roles, pumping in around 8,000 troops and bringing Nato forces in Afghanistan to about 20,000.
The alliance claims to have inflicted grave insurgent losses, including more than 250 in an offensive near Kandahar this month. But at least 35 British and Canadian soldiers have died in a little more than a month, and militants show no signs of giving up.