At least 40 people have been killed in a day of fighting between Lebanese troops and gunmen from a Palestinian refugee camp in northern Lebanon.
Dozens have been killed on a day of gun battles
Some 15 fighters from the radical Fatah al-Islam group and 23 Lebanese soldiers died in intense battles, reports said.
Fatah al-Islam, said to be linked to al-Qaeda, killed some 15 soldiers in clashes around the Nahr el-Bared camp.
Soldiers then bombarded militants in the camp and fought battles at a house in Tripoli used as a base by fighters.
Two civilians were killed and 40 were injured, AFP news agency reported. A Lebanese army spokesman said another 27 soldiers were injured.
Lebanon is home to more than 350,000 Palestinian refugees, many of whom fled or were forced to leave their homes when Israel was created in 1948.
The military is banned from entering the Nahr el-Bared camp under a 38-year-old deal.
Sunday's violence was the bloodiest internal fighting Lebanon has seen since the end of its civil war more than 15 years ago.
Fighting erupted on Sunday morning after security forces raided a building in Tripoli to arrest suspects in a bank robbery.
After resisting arrest, militants said to belong to Fatah al-Islam then attacked army posts at the entrances to the Nahr el-Bared refugee camp, which is home to some 30,000 displaced Palestinians.
Several hours later a large force of Lebanese troops hit back at Fatah al-Islam, storming the building on the outskirts of Tripoli and killing a number of militants.
Fatah al-Islam spokesmen portrayed the fighting as an unprovoked aggression by the Lebanese army.
"The problem began with repeated arrests of our brothers in Tripoli. We've always defended Sunnis in Lebanon," a spokesman called Abu Salim told al-Jazeera TV.
Fatah al-Islam is a radical Palestinian splinter group alleged to have links with al-Qaeda. Lebanese officials also believe it has ties to Syrian intelligence.
Other Palestinian groups have distanced themselves from Fatah al-Islam, which emerged last year after splitting from a Syrian-backed Palestinian splinter group, says the BBC's Beirut correspondent Jim Muir.
After the violence broke out, Syria temporarily closed two border crossings with northern Lebanon because of security concerns.
Some link the eruption in violence to moves at the UN Security Council to set up an international tribunal to try suspects in the assassination of the former Prime Minister, Rafik Hariri, two years ago, our correspondent says.
Syria is against the tribunal, and some Lebanese government sources have accused Damascus of trying to stir up trouble to head it off.
Lebanon's Prime Minister, Fouad Siniora, said Fatah al-Islam was making a deliberate attempt to destabilise the country.
The Nahr el-Bared camp has been under scrutiny since two bus bombings in a Christian area of Beirut in February, blamed on Fatah al-Islam militants based in the camp.