Fighting between the Lebanese army and Islamic extremists has been raging around a Palestinian refugee camp in north Lebanon. The death toll has climbed to more than 50 since the gunbattles started Sunday. VOA Correspondent Challiss McDonough has more from our Middle East bureau in Cairo.

Smoke billows from Nahr al-Bared Palestinian refugee camp in north Lebanon, 21 May 2007

The fighting between the Lebanese army and Fatah al-Islam militants began early Sunday and has intensified dramatically. The army sent in hundreds of reinforcements, and tanks pounded the camp with artillery shells.

A spokesman for the Sunni militant group told Western news agencies that they would expand the battle outside Tripoli if the army did not stop bombardment of its stronghold.

Reports from inside Nahr al-Bared said camp residents were taking shelter in their homes as the fighting raged on.

[Meanwhile, an explosion has rocked a Muslim neighborhood in Lebanon's capital, as Lebanese troops and Islamic militants continue to fight fierce battles at a Palestinian refugee camp to the north.

Television footage showed widespread damage late Monday in the Muslim district of Verdun in western Beirut. Witnesses say the blast set cars ablaze and damaged buildings.

Police say at least six people were wounded.

On Sunday, an explosion in a Christian sector of Beirut killed one person and wounded at least 10 others.]

It is not clear how many civilians have been caught in the crossfire. A brief cease-fire was called to allow ambulances to reach some wounded people, but it quickly came to an end as fighting flared again.

Sami Baroudi is a political science professor at the American University in Beirut. He says for months there have been concerns about Lebanon's fragile security situation and reports that extremist groups have been arming themselves and infiltrating the area.

"Somehow we were expecting something like this to happen, but not at all at this scale," he said. "I think even the army, the intelligence, have been really surprised by the scale of it, by the extent of the coordination. So while clearly this is the work of a terrorist group, I think everybody underestimated how much it could do in one blow."

Smoke is seen above Palestinian refugee camp of Nahr Al-Bared near Tripoli in northern Lebanon, 21 May 2007

This is the worst outbreak of internal violence since the end of Lebanon's civil war.

It comes at a time when, most analysts say, the Lebanese government is extremely weak. Politics have been deadlocked for six months over a proposed international court to try suspects in the 2005 assassination of former Prime Minister Rafik Hariri. Several Lebanese cabinet ministers have said they believe Fatah al-Islam is trying to derail the court on behalf of Syria, which opposes it.

The government has previously leveled that same allegation at Lebanese political opposition parties, led by the armed Shiite group Hezbollah.

The 12 Palestinian refugee camps in Lebanon have been off-limits to Lebanese authorities since 1969 under an agreement with Palestinian leaders. That has created a security vacuum in the camps, which has been exploited by a growing number of extremist groups.

Baroudi says Palestinians living in the camps - and their Lebanese neighbors - have been ripe for recruitment.

Given the overall situation among the Palestinians, if you deal with one fundamentalist group, then in a couple of months it will reappear under a different name, there will be other groups as long as you have thousands of Palestinians who are armed, in camps, who do not have much hope of returning to Palestine, who are heavily ideologized...," he said. "So given the socio-economic political conditions in and surrounding the camps, they are really fertile grounds for the appearance of groups like Fatah al-Islam and dozens of other movements.

The Lebanese government has accused Fatah al-Islam of having ties to both al-Qaida and the Syrian intelligence service. Syria is denying any connection to the group, and Fatah al-Islam denies that it is serving any country's agenda.

The group's leader, Shakir al-Abssi, was apparently released from a Syrian prison last year before moving to Lebanon and setting up the group's base in the Nahr al-Bared refugee camp.

Abssi and the Jordanian-born al-Qaida militant Abu Musab al-Zarqawi were both convicted in absentia in Jordan last year and sentenced to death for the 2002 murder of a U.S. diplomat.