A man in an Afghan army uniform shot and wounded five coalition troops in eastern Afghanistan, the US-led NATO coalition said.
The service members were being treated at a medical facility, the coalition said in a statement on Wednesday.
Colonel Jimmie Cummings, a spokesman for the 130,000-strong coalition force said: "An individual wearing Afghan army uniform turned his weapon on coalition soldiers yesterday [Tuesday], wounding five."
"The wounded coalition soldiers were evacuated to a medical facility."
Dawlat Waziri, an Afghan defence ministry spokesman, confirmed the incident in Maidan Wardak province, a troubled region south of Kabul and said the attack took place inside a military base shared by Afghan and NATO troops.
"A man wearing our army uniform opened fire on the coalition soldiers, wounding five soldiers. The attacker fled the area and we're investigating the incident," Waziri said.
It was the latest likely case of an insider attack on coalition troops.
Three British soldiers were killed on Sunday by an Afghan policeman in southern Afghanistan's Helmand district.
That attack brought the total number of so called "Green-on-Blue" killings involving Afghan security officials attacking NATO allies to 26 in 18 incidents so far this year.
That compares with 11 fatal attacks and 20 deaths the previous year. In 2007 and 2008 there were a combined total of four attacks and four deaths.
Officials do not routinely report such attacks where troops are wounded unless asked.
Efforts to drawdown the number of US and other foreign troops in Afghanistan rely on them working closely with their Afghan partners to train and mentor them so that they can take over the security of their country by the end of 2014.
But such insider attacks fuel distrust and have triggered increased security protections for foreign troops serving in Afghanistan.
A total of 220 foreign troops have been killed this year, including five in July.