A suicide car bomber killed 13 American troops in the Afghan capital Kabul on Saturday, the deadliest single ground attack against the NATO-led force in 10 years of war in Afghanistan.
"We can confirm that 13 International Security Assistance Force members have died," said a spokesman for the International Security Assistance Force (ISAF) in Kabul, giving no further details.
A Pentagon spokesman later confirmed all 13 soldiers killed were American.
Three civilians and a police officer were also killed in the attack on a convoy of military vehicles, a spokesman for the Afghan interior ministry said.
Excluding aircraft crashes, it was the deadliest single incident for foreign troops since the war began in 2001.
Lethal attacks are relatively rare in heavily guarded Kabul, compared with the south and east of Afghanistan, but Saturday's killings came less than two months after insurgents launched a 20-hour assault on the US embassy in the capital.
The assault on the ISAF convoy took place late in the morning in the Darulaman area in the west of the city, near the national museum.
The former royal palace, now in ruins, is also in the area, along with several government departments, and Afghan and foreign military bases.
The Taliban later claimed responsibility for the attack, saying they packed a four-wheel-drive vehicle with 700 kg of explosives.
The Afghan government and its foreign backers are preparing for the end of 2014, the deadline for foreign combat troops to return home.
Some Afghans fear their own security forces will be unable to cope with the insurgency and the country may fall into civil war. Coalition forces have already started handing over responsibility for security to Afghan forces in some parts of the country.
"We are confident we can undertake the transition," NATO's senior civilian representative in Afghanistan, Simon Gass, said at a meeting in Kabul on Saturday before the attack. "If we compare the security situation to how it was two years ago, we can see very dramatic improvements in many areas."
Also on Saturday, three Australians and an Afghan linguist were killed in Uruzgan province in southern Afghanistan when an attacker wearing an Afghan National Army uniform opened fire on them, authorities in neighbouring Kandahar province said.
Violence across Afghanistan is at its worst since the start of the war 10 years ago, according to the United Nations, despite the presence of more than 130,000 foreign troops.
ISAF says there has recently been a fall in attacks by insurgents but this data excludes attacks that kill only civilians and attacks on Afghan security forces operating without international troops.
On Thursday, insurgents armed with rifles and rocket-propelled grenades attacked two bases used by foreign troops in southern Afghanistan. An Afghan interpreter working for ISAF was killed in that attack, which stretched into Friday before the last of the four insurgents were killed.
There has been a series of high-profile assassinations, as well as day-to-day attacks by Taliban raiders, over the past year.
More than a dozen people were killed in the September attack on the US embassy and ISAF headquarters.