NABATIYEH, Lebanon (AP) _ Guerrillas attacked an Israeli-backed militia position with mortar fire Thursday, provoking return fire that wounded two civilians in southern Lebanon, security sources said.

The guerrillas lobbed about three dozen 120mm mortar rounds into the Shoumariyeh outpost on the edge of Israeli's self-styled ''security zone'' in southern Lebanon, the sources said, speaking on condition of anonymity.

Israeli troops and surrogate South Lebanon Army militia struck back with a barrage of 155mm howitzer fire on the Shiite Muslim village of Zawtar, wounding two men, said the sources.

No group claimed responsibility for the mortar attack. The sources did not say if any militiamen were wounded.

The SLA command warned it will shell Lebanese army positions facing the zone unless the army stops guerrillas from firing Katyusha rockets and mortars in the area.