The soldiers were killed in two separate blasts in the volatile southern region, the NATO-led International Security Assistance Force (ISAF) said in a statement.
With 47 US soldiers killed in August, this month has been the deadliest for US forces since their invasion in late 2001 toppled the Taliban government.
More than 300 foreign troops have lost their lives this year, more than in any other year since the invasion.
McChrystal, in a strategic review of the war with Taliban and their associates in Al Qaeda, called the situation 'serious' but said 'success is achievable and demands a revised implementation strategy, commitment and resolve, and increased unity of effort'.
Under US President Barack Obama's new strategy more than 20,000 additional US troops were sent to Afghanistan to reverse gains made by the Taliban and to help create a functioning government.
The new soldiers also helped provide security for country's nationwide elections Aug 20, the results of which have yet to be announced.
Incomplete figures provided by election commission Monday showed that President Hamid Karzai had polled 45.9 percent, leaving him more than 12 percent of his nearest rival, former foreign minister Abdullah Abdullah.
Initial results are expected next week. Should the winner fail to gain an absolute majority, a runoff between the top two candidates will take place in October.
