MARJAYOUN, Lebanon (AP) _ Muslim fundamentalist guerrillas attacked Israeli-backed militia in southern Lebanon on Wednesday, setting off mortar and artillery duels that killed three Lebanese villagers and wounded four.

The Iranian-backed Hezbollah group said its guerrillas blasted an outpost of the South Lebanon Army militia with rocket-propelled grenades and machine- gun fire.

Security sources said there were no casualties in the early evening attack on the SLA outpost in Shoumariyeh, which is in the Israeli-controlled zone in southern Lebanon.

Shortly afterward, a roadside bomb exploded as an SLA patrol drove by, injuring a militiaman, said the sources, who spoke on condition of anonymity.

Israeli and SLA artillery gunners fired on suspected guerrilla hideouts near a cluster of villages fronting the Israeli-controlled zone, the sources said.

U.N. sources, requesting anonymity, said a shell landed on a house in the village of Froon in an area policed by Finnish U.N. peacekeeping forces. U.N. forces have been in Lebanon since Israel's invasion in 1978.

There were no casualties among the peacekeepers, but the sources said a villager, Hassan Hayek, 35, his wife Dalal, 25, and their neighbor Munir Haidar, 50, were killed. Four other villagers were wounded.

The woman was five months pregnant with twins, the sources said.

The clashes came after an announcement that Secretary of State Warren Christopher would travel to the Middle East next week to try to revive stalled Arab-Israeli peace talks.

Violence usually escalates in southern Lebanon, the only active Arab- Israeli war front, when a new peace talks seem imminent or a U.S. official is due to visit the region.

Hezbollah and allied radical Palestinian groups have vowed to wreck the peace process.

Earlier Wednesday, U.S. Ambassador Mark Hambley met with Lebanese Foreign Minister Faris Bweiz in Beirut and said calm in southern Lebanon was essential for the resumption of the peace process.

President Elias Hrawi met with Syrian President Hafez Assad in Damascus on Wednesday to discuss Christopher's visit and the Mideast peace process, government media said.