Four American soldiers were killed by a roadside bomb in Afghanistan on the same day as the first British loss of the year.
Nato said they were attacked yesterday in the south, but did not give further details on the location or their branch of service.
The deaths are the first US fatalities from hostile action in Afghanistan this year. One US service member has died of non-combat causes so far in 2010.
The British soldier died while on foot patrol yesterday in Helmand province.
Afghan insurgents are increasingly turning to roadside bombs in their fight against Afghan and international forces.
Of the 304 US military deaths in Afghanistan last year, 129 were due to IEDs.