At least 13 US soldiers and four civilians were killed when a suicide car bomber attacked a convoy in the Afghan capital, Kabul.
The attack on the International Security Assistance Force (ISAF) convoy took place in the Darulaman area in the west of the city, near the national museum.
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.
The attack was the deadliest against foreign troops in Kabul in recent years.
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.
In the most spectacular recent attack, insurgents launched a 20-hour assault on the US embassy and ISAF headquarters in Kabul in September.
More than a dozen people were killed in that assault.
