A man wearing Afghan security forces uniform shot dead three NATO-led soldiers on Saturday in the eastern part of the country, the coalition said.

"Three International Security Assistance Force (ISAF) service members died when an individual wearing an Afghan National Security Forces uniform shot them in eastern Afghanistan today," an ISAF statement said, adding that both ISAF and Afghan officials were investigating the incident.

So-called "insider attacks", in which Afghan soldiers turn their guns on their foreign partners, have seriously undermined trust between NATO coalition forces and their Afghan allies.

There are presently some 87,000-strong US-led forces fighting alongside about 350,000 Afghan security forces to repel a bloody Taliban insurgency which has been going since 2001.