Five people were killed and six injured in overnight clashes at south Lebanon's restive Ain Al Hilweh Palestinian refugee camp.
Clashes inside the camp left “one dead and six camp residents injured, including children”, said Mounir Makdah, a senior official in Palestinian President Mahmoud Abbas's Fatah movement.
“We are working … to end the clashes and hand over those involved in the incident,” he said.
Clashes between rival groups are common in Ain Al Hilweh, which is home to more than 54,000 registered Palestinian refugees who have been joined in recent years by thousands of Palestinians fleeing the conflict in Syria.
“An Islamist from Al Shabab group was killed, and a leader in the group was among the wounded,” said a Palestinian source inside the camp.
The death toll later rose to five, with two children among the wounded.
Factions used assault rifles and rocket-propelled grenade launchers in the overcrowded camp, as ambulances zoomed through its narrow streets to take the wounded to the hospital, AP reported.
Several residents fled to nearby neighbourhoods in the camp to avoid the gunfire.
The clashes pitted members of Fatah against Islamist groups at the camp, which is located near the coastal city of Sidon, the source said.
The incident happened about two months after similar clashes at the same camp saw a Fatah member killed.
Lebanon's official news agency NNA said “an assassination attempt targeting an Islamist activist” rocked the camp on Saturday, without reporting any casualties.
By long-standing convention, the Lebanese army does not enter Palestinian refugee camps in the country, leaving the factions themselves to handle security.
That has led to lawless areas springing up in many camps, and Ain Al Hilweh has gained notoriety as a refuge for extremists and fugitives.
In March, one person was killed and several others wounded in overnight clashes in the camp, also between members of Mr Abbas's Fatah movement and Islamist groups.
More than 450,000 Palestinians are registered with UNRWA, the Palestinian refugee agency, in Lebanon.
Most live in 12 official refugee camps, often in squalid conditions, and face a variety of legal restrictions, including on their employment.