Four US soldiers have been killed by a roadside bomb in eastern Afghanistan, the Nato-led international force says, BBC reported.
US military spokesman Lt Robert Carr confirmed the four were American soldiers. No further details were released about the deaths.
More foreign troops have been killed in July than in any other month since the US-led invasion of Afghanistan in 2001.
The spike in violence comes ahead of presidential and provincial council elections on 20 August.
Meanwhile, the family of a US soldier held captive by the Taliban in Afghanistan say they have been "overwhelmed with the outpouring of support and concern" they have received.
Pte Bowe Bergdahl, who went missing from his base in a Taliban stronghold near the Pakistani border last month, was shown in a Taliban video on Sunday.
In the video, he said US troops are suffering from low morale and should be brought home "where we belong".
The 23-year-old from Ketchum, Idaho, is believed to be the first soldier seized in either Iraq or Afghanistan for at least two years.