Two foreign soldiers and 14 militants have been killed in the latest clashes in the most serious spell of violence in Afghanistan since the Taliban were overthrown in 2001.
The latest bloodshed came as the US-led coalition announced a major offensive against the Taliban in their southern heartland ahead of handing over the region to NATO troops to allow a reduction in US forces in the country.
An American soldier died in an ambush in the southern province of Helmand on Tuesday, said Major Quentin Innes, a spokesman for international forces in southern Afghanistan.
The ambush triggered a fierce clash in which coalition forces backed by helicopters and planes attacked Taliban positions.
"We believe 12 suspected Taliban were killed in the bombing," Maj Innes said, adding that the coalition was assessing if there were any civilian casualties in the air strikes.
The US military said another foreign soldier had been killed in the eastern province of Kunar yesterday but did not give his identity.
Two Taliban fighters were killed in a gunbattle in the restive province of Zabul after they ambushed a US convoy, wounding two American soldiers.
Taliban officials could not be immediately contacted.
Almost 40 foreign soldiers have been killed in combat in Afghanistan this year, nearly 30 of them Americans.
They are among more than 900 people killed this year, more than 400 in May. Several thousand civilians have fled their homes in the south, fearing more fighting.
The Taliban are mostly active in the south and east where they still enjoy considerable popular support.