The killings came during a day of heavy clashes between the Islamist Jund al-Sham and its Fatah rivals inside the camp, which is outside the control of the Lebanese authorities, with Palestinian factions in charge of security.

Violence broke out early in the day when a Jund al-Sham member, Issam al-Beqaai, was shot dead in his father's clothing store.

Palestinian officials said Beqaai's death may have been a vendetta killing, following a shooting 10 days ago between Beqaai and another man thought to be close to the secular Fatah faction.

After Beqaai's shooting, clashes broke out between fighters using machine-guns and rocket-propelled grenades.

The army took up position at the camp's entrance, just metres (yards) away from the fighting, as dozens of panicked families fled.

Several rockets landed in a residential area outside the camp, but no casualties or damage were reported.

A second Jund al-Sham member, Ahmed al-Hassan, was killed according to Munir Maqdah, the Fatah commander in the camp who heads a multi-factional security committee.

The fighting subsided after calls were made over mosque loudspeakers urging gunmen to cease fire, but later on, a Fatah leader was shot dead in the camp, a Palestinian official said.

"Mohammed el-Saadi was riddled with bullets by an unknown person as he was in a cafe in the camp," said the official. "He died instantly."

Ain el-Helweh has been the scene of recent clashes between Fatah and Jund al-Sham, a Sunni Muslim group of mainly Lebanese without a clear hierarchy.

Extremists believed to have links with Al-Qaeda have settled in Lebanon's Palestinian refugee camps, especially in Ain el-Helweh which has a population of more than 45,000.

Last summer, more than 400 people were killed in a 15-week battle in the northern Nahr al-Bared camp before the Lebanese army expelled Islamists holed up there. -AFP