A majority of families from a besieged Palestinian refugee camp caught in the crossfire between Islamic militants and the Lebanese army have fled but thousands remain trapped inside, a U.N. official said Sunday.

The Nahr al-Bared camp, located near the outskirts of this northern Lebanon port city, was calm Sunday after sporadic gunfire overnight between the army and Fatah Islam militants inside punctured a four-day-old truce.

Hoda al-Turk, a spokeswoman for U.N. Relief and Works Agency for Palestinian Refugees, known as UNRWA, said more 5,000 refugee families — or about 25,000 refugees — have left the camp since the fighting began one week ago. The camp is home to about 31,000 people.

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A majority of the families have fled to the nearby Beddawi refugee camp, while others are staying in Tripoli and other villages, she said.

In a videotape obtained Saturday by AP Television News in Tripoli, the head of the Fatah Islam, Shaker Youssef al-Absi, said his fighters would not surrender but would kill those who storm the camp.

"We wish to die for the sake of God ... Sunni people are the spearhead against the Zionist Americans," said the bearded leader, who is suspected of having ties to Al Qaeda. He was shown seated before a black banner, as another militant holding a machine gun stood next to him. The tape also showed militants training in an unidentified camp.

The Lebanese government has vowed to crush the militants. The military has rolled more troops around the camp, which is already ringed by hundreds of soldiers, backed by artillery and tanks. Fatah Islam has claimed to have more than 500 fighters with automatic weapons, mortars and rocket-propelled grenades, inside the camp.

Three U.S. transport planes carrying military aid arrived from Kuwait on Saturday in an effort to help shore up the army. So far, eight military transport planes have landed at Beirut airport since Thursday — four from the U.S. Air Force, two from the United Arab Emirates and two from Jordan. Media reports said the planes carried ammunition, body armor, helmets and night-vision equipment.

U.S. arms are a sensitive issue in a nation deeply divided between supporters of Prime Minister Fuad Saniora's government and an opposition backed by America's Mideast foes, Iran and Syria. The Shiite Hezbollah-led opposition accuses Saniora of having too close ties to Washington.

Hezbollah leader Sheik Hassan Nasrallah criticized the American aid, saying Friday that Lebanon was being dragged into a U.S. war against al-Qaida that would destabilize the country, and warning the military against attacking Nahr al-Bared.

Saniora defended the U.S. aid, telling the Arabic-service of the British Broadcasting Corp. that the aid was not a "crime" and that the weapons had been offered by different countries a year ago.

Palestinian factions, meanwhile, have been scrambling to find a negotiated solution to end the siege and avert what many fear would be a bloody battle between the Lebanese army and the Fatah Islam.

An all-out army assault could spark violence elsewhere in Lebanon, host country to some 400,000 Palestinian refugees who mostly live in camps that are rife with armed groups.

The U.S. military aid could inspire other militants into what they perceive as an all-out battle against the West.

At least 20 civilians and 30 soldiers have been killed in the fighting. The Lebanese military says 60 Fatah Islam fighters were killed, though the group put the toll at 10.

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