A Palestinian security force fanned out Wednesday in two neighborhoods of this refugee camp in southern Lebanon to prevent further clashes between Islamic militants and Lebanese troops.

Sporadic exchanges continued in northern Lebanon, where the army is fighting Fatah Islam militants barricaded in the Palestinian refugee camp of Nahr el-Bared.

The violence in the north, which began May 20 and intensified last week, threatens to spread to other Palestinian camps in Lebanon and beyond.

Four bombs have exploded in the Beirut area since the fighting began, killing one person and wounding more than 40 people. A bomb was found and dismantled Wednesday on a public beach in the southern port city of Tyre.

Three people -- two soldiers and a militant -- were killed in clashes Sunday and Monday between Jund al-Sham Islamic militants and Lebanese troops ringing Ein el-Hilweh, the largest of the 12 camps with about 65,000 residents. Jund al-Sham is sympathetic to Fatah Islam.

Most of the clashes happened in the Taamir and Taware neighborhoods. where the fighting has since died down. In a bid to keep the calm, some 40 men armed with automatic rifles took up positions in the two neighborhoods on Wednesday, a force drawn from the camp's various factions -- secular and Islamic extremist.

Under a nearly 40-year-old arrangement granting Palestinians authority to rule themselves, Lebanese troops do not enter the camps -- crowded towns with schools, clinics and markets that have also harbored militants and outlaws.

Loudspeakers on the minarets of mosques urged people to reopen stores and resume normal life in the camp. Some of the several thousand refugees who had fled the fighting to nearby areas of Sidon, the provincial capital of southern Lebanon, began returning Wednesday.

The army reopened its checkpoints around the camp for traffic.

Major Palestinian factions have been trying to mediate an end to the battle.

The Fatah faction of Palestinian President Mahmoud Abbas was trying to persuade Palestinians at Nahr el-Bared who sided with the militants to abandon the fight.

Maj. Gen. Khaled Aref, a senior Fatah commander based in Ein el-Hilweh, said Wednesday on Lebanese Broadcasting Corp. television that about 20 Fatah Islam fighters had surrendered to his group in besieged Nahr el-Bared.

The surrenders would mark the first time a major Palestinian group responded to calls by Lebanese authorities to campaign against Fatah Islam.

Abbas has denounced the militants, whose few hundred members embrace al-Qaida-style militancy and doctrine and are suspected of having links to Osama bin Laden's network.

More than 100 people have been reported killed in the fighting, the worst internal violence since the end of Lebanon's 1975-90 civil war.

Among the dead were 45 soldiers, including 10 killed since the military launched its offensive Friday at Nahr el-Bared and the two who died in the clashes at Ein el-Hilweh. About 60 Fatah Islam militants were believed killed.

At least 20 civilians have been reported dead at Nahr el-Bared, but any recent civilian casualties were unknown. Most of the camp's 31,000 residents have fled, but about 5,000 remained.