NATO says four international service members were killed Sunday in an insider attack “suspected to involve members of the Afghan police” in southern Afghanistan.

The alliance did not provide further details. A series of insider attacks have occurred across Afghanistan in recent months.

In another development, international coalition officials say the insurgents who attacked a British military base in Afghanistan Friday, killing two U.S. Marines, were dressed in U.S. Army uniforms and were armed with automatic rifles, rocket propelled grenade launchers and suicide vests.

The coalition said Sunday the 15 militants were organized into three teams and “executed a well-coordinated attack” against the airfield on Camp Bastion in Helmand province.

The alliance say the attackers destroyed six Harrier jets and “significantly damaged” two more.

The militants also destroyed three coalition refueling stations and damaged six aircraft hangars.

International troops killed 14 of the insurgents and wounded one, who is in custody. Earlier reports said 18 militants died in the attack.

In addition to the two U.S. Marines killed in the assault, eight military members and one civilian contractor were wounded.

The Taliban has claimed responsibility for the attack.