An Afghan soldier on Thursday killed two NATO troops after opening fire on members of the US-led International Security Assistance Force, the military said.

"An individual wearing an Afghan National Army uniform turned his weapon against International Security Assistance Force service members in eastern Afghanistan today, killing two service members," ISAF said.

ISAF did not identify the nationalities of the dead soldiers and gave no further details of the incident, which came on the third day of fierce protests against the burning of the Koran at a US-run military base.

Asked whether the events were connected, an ISAF spokesman would only say: "There was a demonstration in the province."

Afghan troops defending a foreign base in eastern Nangarhar province had "joined demonstrators and opened fire on foreign troops", a protester told the Afghan Islamic Press news agency.