Al Jazeera's Zeina Khodr said: "Busloads of civilians are being evacuated ... some of the people who are fleeing are injured and require urgent medical treatment. They are being taken to hospitals into the northern city of Tripoli."
UN officials in the Beddawi camp about 10km away said they expected 10,000 refugees to arrive through the night.Humanitarian concerns
Ibrahim Issa Dawoud, who left the camp with his wife and six children, said: "We thought this was our last chance because they will bulldoze the camp. That is why we took the risk and fled."
The truce appeared to have collapsed when a UN aid convoy that had been allowed into the Nahr al-Bared came under fire.
Four Palestinian civilians were killed and at least six critically injured before the trucks were forced to pull out.
The convoy had waited for hours outside the camp near Tripoli as humanitarian organisations warned of disaster if food, water and medicines did not reach the refugees soon.
"From outside it's very easy to condemn the Lebanese army and government for what they are doing against Fatah-al-Islam"
Rabih, Mansourieh El Metn, Lebanon
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The 40,000 Palestinians living in Nahr al-Bared are reportedly running out of supplies as the refugee camp remains virtually under siege.
"There is very clearly a big demand for assistance in the camp at the moment. Water is a major issue, food and medical supplies will be a major issue very soon," Sven Berthelsen of UNRWA, the agency that cares for Palestinian refugees, told Al Jazeera.
"We are very concerned about the potential spread of disease as sanitational systems are not functioning problems and water supplies are not adequate."
He added that the agency would try again on Wednesday to get aid to the people trapped in the camp.
Medical sources have been calling for a halt to the fighting so they can reach the dead and wounded on the streets.
Omar Keenan, a doctor in one of the camp's medical centres, told Al Jazeera the situation was a "disaster".
"There are severe casualties. We are in need of blood, our blood bank is empty. We are performing operations on the floor. These medical centres have come under fire and people are crying out for help. We have no ability to cope. The number of casualties is in the hundreds.
More than 80 people since Sunday have been killed in the country's worst internal violence since the 1975-1990 civil war.
Elsewhere in Tripoli on Tuesday, a member of Fatah al-Islam blew himself up as security forces raided a building in the northern city, a senior security official said.
|The Lebanese army erects a sand |
barricade inside the camp [AFP]
The man detonated an explosives belt after officers ordered him to surrender in the northern neighbourhood of Mitayn, the official said on condition of anonymity.
Sheikh Salim Lababidi, mufti of Palestinians in Lebanon and the diaspora, appealed through Al Jazeera for the world to open its eyes to what is going on in the camp in Lebanon.
He said: "People inside the refugee camp have contacted me, saying that more than 100 civilians have been killed and injured in the camp.
"We have all denounced the killing of army soldiers, but no one has denounced the killing of dozens of these civilian Palestinians. Why are they being killed and shelled?"
Sultan Aboul Aynan, the Lebanon chief of the mainstream Fatah from which Fatah al-Islam splintered off, called for a halt to the army's bombardment, warning that civilians were paying the price for the actions of "a gang of outlaws".
Ban Ki-moon, the UN secretary-general, condemned the attack on the UN aid convoy and demanded an end to Fatah al-Islam's attacks on the Lebanese army.
"These actions constitute an assault on Lebanon's stability and sovereignty, and have seriously endangered civilians. They must halt immediately," Michele Montas, Ban's spokeswoman, said in a statement.
The Arab League condemned the "criminal and terrorist acts committed by the so-called terrorist group Fatah Islam against the army, Lebanese security forces and innocent citizens."
It added that it supported the efforts the Lebanese government's efforts to root out the group
Javier Solana, the European Union foreign policy chief also defended the actions of Lebanon's military in the refugee camp, saying Lebanon was fighting a "terrorist group".
The US state department has said that it is considering providing financial help to the Lebanese army.
"Right now we are considering a request for additional assistance coming from the Lebanese government. The Lebanese armed forces are engaged in a tough fight against a brutal group of violent extremists," Sean McCormack, state department spokesman, said.