Three people were killed in clashes overnight and into Tuesday morning between rival armed groups in Lebanon's largest Palestinian refugee camp, near southern Sidon, medical sources told AFP.
The fighting between the Jund al-Sham Islamist group and members of Palestinian President Mahmud Abbas's Fatah movement prompted hundreds of residents to flee Ain al-Helweh camp and shelter in nearby mosques.
Medical sources said at least 35 people were wounded, with ambulances unable to enter the camp to retrieve other injured people because of the heavy clashes.
At least two of the dead were Fatah members, one of them an officer, Palestinian sources said. The identity of the third person was unclear.
The sound of fierce gunfire and rocket fire could be heard in neighbouring Sidon, and the Lebanese army reinforced its positions at the four main entrances to Ain al-Helweh.
It was allowing those able to reach the entrances to leave the camp, but preventing anyone from entering, an AFP correspondent said.
The clashes first broke out on Saturday after two Fatah members were killed during an apparent assassination attempt by Islamists on a leading Fatah official.
They continued sporadically throughout the weekend.
Tensions have been running high for months between Palestinian factions and Islamists inside Ain al-Helweh, an impoverished and overcrowded camp.
By long-standing convention, the army does not enter Palestinian refugee camps in Lebanon, leaving the factions themselves to handle security.
That has created lawless areas in many camps, and Ain al-Helweh has gained notoriety as a refuge for extremists and fugitives.
But the camp is also home to more than 54,000 registered Palestinian refugees who have been joined in recent years by thousands of Palestinians fleeing the fighting inSyria.
More than 450,000 Palestinians are registered in Lebanon with the UN agency for Palestinian refugees UNRWA.
Most live in squalid conditions in 12 official refugee camps and face a variety of legal restrictions, including on their employment.