Four Afghan soldiers involved in a coalition-led operation against militants have been killed by a bomb in eastern Kunar province, officials say.
Operation Mountain Lion is targeting various militant strongholds along the border
Another three are reported to have been hurt in the blast in Sawkey district.
The BBC's Bilal Sarwary in Kabul says this was the biggest loss for the Afghan army since the start of Operation Mountain Lion.
It comes a day after the US said three suspected militants died in an air strike in southern Helmand province.
On Tuesday Afghan officials also said five insurgents had been killed in fighting with Afghan police after suspected Taleban militants attacked a police station in Kandahar province.
In another incident on Tuesday evening, two civilians were hurt in a rocket attack near the US embassy in Kabul, police said.
Operation Mountain Lion involves around 2,500 US and Afghan forces targeting suspected Taleban militants along the border with Pakistan.
Targeting the Taleban
The incident in Sawkey district happened on Tuesday night as an Afghan National Army vehicle was passing through the area.
The governor of Kunar province, Assadullah Waffa, told the BBC the roadside bomb was "the work of the enemies of Afghanistan".
On Tuesday coalition aircraft fired missiles and a bomb at a meeting of suspected militants in Lashkar Gah district in Helmand province, the US military said.
A military statement said there was no damage to civilians or property.
Helmand province has been at the centre of a recent upsurge in fighting. The Taleban has threatened a spring offensive against foreign forces.
The US military said the people killed in the air strike were "responsible for launching numerous attacks against the Afghan government and coalition forces including financing terrorist activities".
There has been an upsurge in violence in southern Afghanistan over the last year, making some parts no-go areas for aid workers.
More than 3,000 British troops are being deployed in Helmand province in the coming months.