Four US soldiers have been killed in an attack in the eastern Afghan province of Kunar, US army reports say, BBC reported.
The soldiers were caught in a "complex attack", the Associated Press news agency quoted US army spokeswoman Capt Elizabeth Mathias as saying.
A number of Afghan soldiers also died in the incident.
Violence in Afghanistan has hit a record high, eight years after the United States-led invasion that toppled the Taliban.
A top district official, Hamisha Gulab Shinwari, told AFP news agency the fighting was continuing.
Deadliest year
The deaths came as it was announced that President Hamid Karzai had gained more than 50% of counted votes in the presidential election held on 20 August.
But the UN-backed Election Complaints Commission in Afghanistan says it has found "clear and convincing evidence of fraud" in the poll and has ordered a number of recounts and ballot audits.
This year has been the most deadly for US troops in Afghanistan since 2001, with 190 soldiers killed.
The previous deadliest year was 2008, when 155 US military personnel died. A total of 1,369 foreign military personnel have been killed in Afghanistan since 2001.
More than 30,000 extra US troops have been sent to Afghanistan since President Barack Obama ordered reinforcements in May, almost doubling his country's contingent and increasing the Western total to about 100,000.