Kabul, Sep 16 (IANS): In the latest so-called "green on blue" attack, four soldiers of the NATO-lead ISAF were killed Sunday by Afghan policemen, a NATO statement said.

"Four International Security Assistance Force (ISAF) service members died today (Sunday) in southern Afghanistan following an insider attack suspected to involve members of the Afghan police," Xinhua quoted the NATO statement as saying.

The attacks are referred to as "green on blue" as green is the colour of the Afghan forces' uniforms, and blue of the American military.

The attack came a day after two British soldiers were shot dead by an Afghan Local Police (ALP) service member in southern Helmand province.

The NATO statement did not disclose the nationalities of the victims nor details about the incident.

Troops mainly from the US, Britain and Australia are stationed in the southern region.

Sunday's attack brings to 33 the number of "green on blue" attacks this year, killing 51 service members with the military alliance.

While NATO officials say only 25 percent of such attacks are related to the Taliban, the terror outfit says their fighters have infiltrated the Afghan army and police in order to kill foreign soldiers.

Late Friday, a group of Taliban, dressed in US military uniforms, launched an attack against a main coalition base -- Camp Bastion in Helmand -- that left two US Marines and 14 Taliban dead.

It was not known whether the attack was related to Taliban's announcement of hunting down Prince Harry, who arrived at Camp Bastion earlier this month, to serve a four-month term as an Apache helicopter pilot.

"The ISAF cannot draw the conclusion that the reasons behind the recent attacks were related to Prince Harry," ISAF spokesman Major Adam Wojack told Xinhua Sunday.

Six coalition AV-8B Harrier jets were destroyed and two were damaged. Three refuelling stations were also destroyed. Six soft-skin aircraft hangars were damaged.