A military commander of the Fatah movement was critically wounded Tuesday in a bomb explosion in Lebanon's largest Palestinian refugee camp, Lebanese and Palestinian security officials said. Talal Sleim was heading to his office in the Ein el-Hilweh camp, on the outskirts of the southern city of Sidon, when a roadside bomb exploded nearby, the officials said. Sleim, a 43-year-old Palestinian, was seriously wounded and was rushed to a Sidon hospital outside the teeming camp, the officials said, speaking on condition of anonymity because they were not authorized to speak to reporters. A bodyguard was also lightly wounded, they said. After news of the explosion spread, Fatah guerrillas exchanged machine gun fire with Palestinian gunmen of the Jund al-Sham group, which follows the extremist ideology of al-Qaida. Tension ran high in the camp with scores of Palestinian families, fearing wide-scale fighting between the two factions, fleeing their homes to safer areas outside the shantytown, witnesses said. Tuesday's bombing came more than a week after three Palestinian militants, including a Jund al-Sham military commander, Shehadeh Jawhar, were killed in clashes with Fatah guerrillas in the camp. Jund al-Sham gunmen vowed to take revenge for Jawhar's killing. Jawhar was a prominent extremist who fought American troops in Iraq. He was wanted by Lebanese authorities for numerous acts of violence. The Jund al-Sham group has in the past clashed with Fatah guerrillas and Lebanese troops deployed around Ein el-Hilweh. It has been blamed or claimed responsibility for a number of bombings and gunbattles in Lebanon and Syria. Jund al-Sham is Arabic for Soldiers of al-Sham _ an old Arabic word for the region of Syria, Lebanon and Jordan. Ein el-Hilweh, with a population of 70,000, is the largest of Lebanon's 12 Palestinian refugee camps. It is a hotbed of Islamic extremists, is notorious for lawlessness and is frequently rocked by gunfights between armed groups jockeying for power. A number of fugitives live in the camp, which is under Palestinian jurisdiction and off limits to Lebanese authorities.