Israeli warplanes attacked guerrilla targets in south Lebanon Monday, the second day of intensifying hostilities on the last active Arab-Israeli war front, security sources said.

Two fighter bombers fired at least two missiles on the northeastern edge of Israel's self-declared security zone at midday, said the sources, speaking on condition of anonymity.Thick black smoke could be seen billowing from the hills and ravines from miles away, the sources said.

Two jets returned 40 minutes later to fire two more missiles at the same area, which is often used by Iranian-backed guerrillas to infiltrate into the Israeli border enclave, the sources said.

The raids, the sixth and seventh this year, came several hours after Hezbollah guerrillas attacked an outpost of Israel's surrogate militia, the South Lebanon Army.

There was no immediate word of casualties.

The escalating violence raised the specter of a major showdown that could further slow down the U.S.-sponsored Middle East peace process.

In the heaviest clashes this year, Hezbollah guerrillas launched simultaneous, pre-dawn onslaughts on 12 Israeli and militia outposts Sunday.

Israeli warplanes struck back with three air raids and artillery attacks on suspected Hezbollah hideouts.

Five people were killed and five wounded in air and ground fighting along a 40-mile front.

In Monday's attack, Hezbollah guerrillas took responsibility for raking a militia outpost with machine-gun fire, rocket-propelled grenades and Katyusha missiles.

Security sources said Israeli and militia forces struck back at Shiite Muslim villages facing the Sojod outpost in the central sector of the enclave with 155 mm howitzer and tank cannon fire.