"The Soldiers reported being attacked with possibly a machine gun near Asadabad of Kunar, and returned fire with mortars," US military said in a statement.
There were no reports of injury or damage.
The attackers fled shortly after the incident. Afghan and US forces are currently conducting a search of the area.
"US forces and their Afghan counterparts often visit remote areas of Afghanistan with doctors and other health-care professionals to help families with their medical needs. These visits are often supplemented with veterinarians who vaccinate livestock against disease," the statement added.
Also in Kunar province, US forces on Monday discovered a weapon cache and detained six people, US military said Tuesday.
"The cache consisted of five grenades, one rocket-propelled grenade, wires and timing devices, hundreds of rounds of ammunition and Taliban propaganda materials," it said.
A four-member US Special Forces troops missed in Kunar on June 28, and one US Chinook helicopter was shot down on the same day by a rocket propelled grenade when it was carrying on the searching operation for the missing US ground team. Altogether 16 US troops including eight Navy SEALs were killed.
Taliban claimed the responsibility for the crash.
US forces carried out the searching operation in the province afterwards, and conducted an air strike Friday against a military compound that resulted in the deaths of some terrorists and civilians.
Kunar governor Asadullah Wafa said that 17 civilians were killed during the bombing, including women and children.