An Afghan soldier turned his weapon on a vehicle he believed was driven by NATO soldiers on a shared base in the south, slightly wounding a foreign civilian worker, officials said Monday. It was the latest in a string of insider attacks by Afghan forces against their international allies.

The attacks by Afghan soldiers and police against international forces are threatening to undermine a partnership that is key to the handover of security responsibility to the Afghan government and therefore to the entire program for the drawdown of international troops.

The Sunday evening attack in Helmand province came the same day an Afghan police officer shot and killed four American service members in Zabul, also in the south. That followed on a shooting Saturday in which a man wearing the uniform of a government-back militia group killed two British soldiers in Helmand.

The soldier turned his weapon on a vehicle that was driving inside Camp Garmser, a shared base in Helmand, said NATO forces spokesman Maj.