Five U.S. soldiers were killed in Afghanistan on Tuesday, NATO said, as the number of Americans to die in the war in the past four days climbed to 22.
Four soldiers were killed in eastern Afghanistan in a Taliban-style bomb attack, NATO's International Security Assistance Force (ISAF) said.
The fifth died in an insurgent attack in the south of the country, where the insurgency is at its fiercest, it said in a separate statement. A spokesman confirmed to AFP that all the dead were Americans.
The deaths bring to 485 the total number of foreign troops killed in the Afghan war this year, compared to 521 for all of 2009, according to an AFP tally based on that kept by the independent icasualties.org website.
Following news of the deaths, U.S. President Barack Obama warned that the United States faced a "very tough fight" in Afghanistan, with more casualties and "heartbreak" to come.
"We obviously still have a very tough fight in Afghanistan," Obama told troops in Fort Bliss, Texas, as he prepared to mark the formal end of the U.S. army's combat operations in Iraq.
"We have seen casualties go up because we are taking the fight to Al-Qaeda and the Taliban," Obama said. "It is going to be a tough slog."
On Monday eight NATO troops -- seven of them American -- were killed in bomb attacks in southern Afghanistan.
The eighth soldier was a 20-year-old Estonian who died of his injuries on Monday after insurgents set off an improvised explosive device (IED) in Nad-e-Ali in Helmand province.
Estonia has a 160-strong contingent within the NATO-led International Security Assistance Force in Afghanistan, part of a troop deployment of almost 150,000 under NATO and U.S. command.
French military officials said Tuesday that a soldier serving in Afghanistan was killed when the armored vehicle he was travelling in tumbled into a ravine.
The vehicle was carrying three French soldiers when it crashed Monday during an operation in the Uzbeen valley in the east of the country conducted with Afghan and U.S. troops, military headquarters in Paris said in a statement.
France has 3,750 troops helping fight Taliban insurgents in Afghanistan in a conflict that has cost 47 French soldiers their lives.
Canada lost its 152nd soldier of the Afghan war when a corporal died from injuries sustained from an IED on August 22. He died in hospital in Germany, the military said.
With most of the boots on the ground, the United States is bearing the greatest burden; however, losing 1,267 soldiers since the war began in late 2001.
Altogether, the coalition has lost 2,053 soldiers in the war.
The insurgency is at its most intense in the southern provinces of Kandahar and Helmand, but it has rapidly spread to other regions in the past year.
NATO is struggling to turn the tide on the Taliban but officials say that the arrival of 30,000 extra troops, as part of Obama's surge aimed at speeding an end to the war, is having an impact.
The U.S. commander of the Afghan war, General David Petraeus, acknowledged Tuesday that the Taliban were expanding their footprint across the country even as foreign forces close in on their traditional southern strongholds.
A sharp rise in attacks on international troops showed the hard-line Islamist militia was feeling threatened in their safe havens after almost nine years of war, he told reporters.
The overall strategy against the Taliban was reaching its "final stages," he told three foreign media organisations including AFP, with the number of U.S. and NATO troops set to peak at 150,000 in the coming days.
"Levels of attacks have gone up and that's a manifestation of us increasing our resources substantially and taking away safe havens that the Taliban have been able to establish over the course of the last several years," he said.
"And when the enemy's safe havens are threatened they fight back."
The insurgency is concentrated in Kandahar and Helmand, which the Taliban consider their heartland, but is becoming increasingly intense along the eastern border with Pakistan.
Northern provinces are also becoming more unstable, as NATO supply lines from Central Asia traverse the previously peaceful region, drawing insurgent fighters who, residents say, are becoming embedded in villages and districts.
ISAF said that three employees of the Afghan Supreme Court were killed and several others wounded when a gunman opened fire on the mini-bus they were travelling in Tuesday in Kabul.
Clinton condemns election-lined killings in Afghanistan
U.S. Secretary of State Hillary Clinton on Tuesday condemned the killings of an Afghan parliamentary candidate and five members of the campaign team for another candidate.
In the western province of Herat, the Taliban was suspected at the weekend of having killed a man running for parliament in elections set for September 18 as well as five members of the campaign team of a female candidate.
Clinton said the "United States strongly condemns" the killing of the candidate and the five election workers.
"Though it is not yet clear who is responsible for these killings, our thoughts and deep sympathies are with the families affected by these horrible attacks," she said in a statement.
Afghanistan, plagued by an increasingly deadly Taliban-led insurgency, is due to hold its second post-Taliban parliamentary elections on September 18 amid fears that attacks might disrupt the vote.
"Violent intimidation of electoral candidates and their supporters undermines the right of all Afghans to a peaceful and democratic future for their country," the chief U.S. diplomat said.
"And those responsible for the killings must be brought to justice," she added.
"Afghanistan's upcoming parliamentary elections are an important milestone on the road to becoming a full and rightful member of the community of democratic nations," Clinton said.
"We encourage the government of Afghanistan to provide adequate security measures that allow candidates and voters, particularly women, to fully participate and ensuring the election process reflects the democratic will of the Afghan people," she said.