A roadside blast Wednesday in eastern Afghanistan killed four U.S.-led coalition soldiers and an Afghan, the coalition said.
It did not identify the nationalities of all the victims, but the majority of troops in eastern Afghanistan are American.
U.S. military deaths in Afghanistan in 2008 have already surpassed the record 111 deaths the U.S. suffered last year, as insurgent attacks have increased.
The number of attacks on U.S. forces in eastern Afghanistan has risen by around 30 percent this year compared with 2007, U.S. military officials say.
The coalition did not say where the Wednesday attack took place or provide any other details.
The deaths came the same day U.S. Defense Secretary Robert Gates held meetings in Kabul with President Hamid Karzai and other officials.
The mountainous eastern region borders Pakistan's tribal areas, where militants train, recruit and arm, and where Afghan and U.S. officials allege that al-Qaida has managed to reconstitute itself after being driven out of Afghanistan following the 2001 invasion that ousted the Taliban from power.
Separately, coalition troops killed two militants and detained two others during a raid in central Afghanistan, a statement said Wednesday. The action happened Tuesday in an operation in the Andar district of Ghazni province.
One of the militants killed had allegedly been involved in attacks against Afghan and foreign troops and civilians, the coalition said.
More than 4,200 people — mostly militants — have died in insurgency-related violence this year, according to an Associated Press tally of figures from Afghan and Western officials.