NAHR AL-BARED, Lebanon (Reuters) – Two relief workers were killed and a Palestinian mediator was wounded in fierce fighting on Monday between Lebanese troops and al Qaeda-inspired militants at a Palestinian refugee camp.

Security sources said the two Lebanese Red Cross workers were killed and a third was wounded when they were hit by a shell during fighting between the army and Fatah al-Islam militants at Nahr al-Bared camp in northern Lebanon.

The Red Cross along with other local and international aid agencies almost daily help civilians flee the camp and take in medical and food supplies. The two slain workers had been at the northern entrance of the camp, the sources said.

In a separate incident, a Palestinian cleric, Sheikh Mohammad al-Hajj, was shot in the thigh by a sniper after he entered the camp to hold talks with the militants on ways to end the 23-day-old conflict.

“I’m alright. The (peace) initiative will continue … to stop the bloodletting,” Hajj told reporters at a hospital in the nearby city of Tripoli before he was taken to the operating room to stitch up his wound.

It was not clear who had shot him.

A cloud of smoke hung overhead as scores of heavy artillery rounds crashed into the camp, while tank and heavy machinegun fire strafed suspected militant hideouts.

The militants hit back with sporadic firing of mortar bombs and rocket-propelled grenades.

At least 132 people have been killed, including 57 soldiers, in three weeks of fighting, the worst internal clashes since Lebanon’s 1975-1990 civil war. Eleven soldiers died and more than 100 were wounded in battles at the weekend alone.

Rescue workers have been unable to give an accurate death toll because of the difficulty of moving in the camp — a sprawling warren of alleyways on the Mediterranean — but at least 42 militants and 33 civilians have been killed.

The army says the militants triggered the conflict by attacking its positions around the camp and on the outskirts of the nearby city of Tripoli. Fatah al-Islam says it acted in self defence and has vowed to fight to the death.

The fighting has further undermined stability in Lebanon, already paralyzed by a seven-month-old political crisis.

Deadly clashes erupted last week in the south at the largest Palestinian refugee camp in Lebanon, and five bombs have targeted civilian areas in and near Beirut since May 20.

Lebanese and Palestinian Islamist politicians and clerics have so far failed to broker an end to the conflict.

Most of Nahr al-Bared’s estimated 40,000 residents have fled to other nearby refugee camps. About 80 more left on Monday.

Some 400,000 Palestinian refugees live in Lebanon, around half in 12 camps.

In eastern Lebanon, security forces arrested four people on suspicion of belonging to an Islamist militant group, security sources said. The arrests were part of a crackdown in the Bekaa Valley following the arrest of three Arab al Qaeda members last week in possession of weapons and explosives.

Monday’s arrests brought to more than 13 the number of people detained in the case.