KABUL, (AFP) — Four coalition soldiers were killed in three separate incidents in Afghanistan Saturday, NATO’s International Security Assistance Force (ISAF) said.

Afghan sources said at least one British soldier died and another was wounded when two Afghan policemen turned their weapons on their allies in a joint base in southern Helmand province.

ISAF said it could not confirm this, but was investigating the reports.

In terse statements, ISAF said two soldiers died following an insurgent attack, one was killed in a bomb blast and another died as a result of a “non-battle related injury” — all in southern Afghanistan.

The statements gave no further details and did not identify the soldiers’ nationalities.

Helmand province police spokesman Farid Ahmad Farhang told AFP that “two Afghan policemen opened fire on British soldiers inside a joint military base in Nahre Saraj district, killing one British soldier and wounding another”.

“The police shooter was also killed when foreign troops returned fire, the second policeman has been injured.”

A senior security official in the province, Mohammad Ismail Hotak, confirmed the attack, saying “at least one foreign soldier” was killed.

An increasing number of Afghan troops have turned their weapons against NATO soldiers who are helping Kabul fight a decade-long insurgency by hardline Taliban Islamists.

Some of the assaults are claimed by the Taliban, who say they have infiltrated Afghan army ranks, but many are attributed to cultural differences and antagonism between the allied forces.

A total of 20 NATO soldiers have been killed by Afghan colleagues in at least 15 separate attacks so far this year, according to an AFP tally.