At least 24 people have died and scores have been injured in clashes between the Lebanon army and an armed Palestinian group around a refugee camp in the north of the country.
At least 29 people have been hospitalised in the wake of the battles between the army and Fatah al-Islam, in and around the city of Tripoli.
The Lebanese army said 13 soldiers and and at least ten Fatah al-Islam fighters had died. A civilian was also reported dead.
Fighting broke out between the army and Fatah al-Islam after security forces raided homes in Tripoli to arrest suspects accused of robbing a bank a day earlier.
A Lebanese military source said the army was blasting the camp with tank fire after regaining control of Tripoli.
More than 40 wounded people have contacted Al Jazeera saying they are not able to leave their homes to reach hospitals.
Witnesses reported hearing exchanges of fire from assault rifles and machine guns, as well as rocket explosions.
Fouad Siniora, Lebanon's prime minister, accused Fatah al-Islam of trying to destabilise the country.
In a statement, he said: "The blows dealt by Fatah al-Islam against the Lebanese army are a premeditated crime and a dangerous attempt to destabilise [Lebanon]."
He called on the people of Lebanon, which has been battling political chaos for months, to "join ranks behind the army and Lebanese security forces".
Earlier, Fatah al-Islam told Lebanon's army not to take "provocative actions" against the group.
The authenticity of the groups' statement could not be immediately verified but its language was similar to previous statements from the group.
"We warn the Lebanese army of the consequences of continuing the provocative acts against our mujahidin who will open the gates of fire... against [the army] and against the whole of Lebanon."
The Lebanese army cannot enter Palestinian refugee camps in line with a 38-year-old agreement.
However, it has tightened its grip around the camp since the authorities charged members of the group with carrying out two bus bombings in a Christian area near Beirut that killed three civilians in February.
The Lebanese army has also stepped up security in the area surrounding Ain al-Hilweh refugee camp in southern Lebanon.
Fatah al-Islam was formed last year by fighters who broke off from the pro-Syrian Fatah-Intifada group.
Lebanese officials say the group is merely a front for Syrian intelligence in Lebanon.
Syria and Fatah al-Islam deny having any relationship.
Fatah al-Islam statements have appeared on Islamist websites known to publish al-Qaeda statements.
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