The NATO-led force released no other details about the deaths, including the troops' military branch or where the attack occurred. Tech Sgt. Chuck Marsh confirmed that the two troops were American.
Southern Helmand province is the site of the largest U.S. Marine operation since the 2001 invasion to oust the Taliban regime . Some 4,000 Marines are taking part. They have met little resistance from Taliban fighters but have had to contend with dozens of roadside bombs hidden in the region's dirt roads.
July has been the deadliest month for U.S. and NATO forces . Wednesday's deaths raised the American toll to 34, surpassing the 28 who were killed in two months last summer.
At least 18 British troops have also died, a toll that has sparked debate in Britain over whether those troops have enough helicopters and other equipment.
The U.S. has close to 60,000 troops in Afghanistan, a record number. President Barack Obama has increased the U.S. focus on Afghanistan as American forces draw out of Iraq.