Fighting has broken out between soldiers and Islamist militants at a second Palestinian refugee camp in Lebanon, security officials say.

The violence in the Ain al-Hilweh camp, near the southern city of Sidon, is said to involve Jund al-Sham militants.

Two people - a soldier and a civilian - were injured when suspected militants fired a grenade at an army checkpoint.

It is not clear if the violence is linked to the fighting at the Nahr al-Bared refugee camp in the north.

Army troops at the Ain al-Hilweh camp responded to the rocket propelled grenade attack with gunfire, witnesses said.

The BBC's Kim Ghattas in Beirut says the Jund al-Sham militants are similar to those fighting Lebanese army troops in the Nahr al-Bared refugee camp.

There the Lebanese army is shelling militant positions deep within the besieged camp to try to force the militants to surrender.

Fighting between the militants and the army began at the camp near Tripoli in northern Lebanon two weeks ago.

More than 100 civilians, soldiers and militants are reported to have died since.

The army says militants from the Fatah al-Islam group have been cleared from the edges of the Palestinian camp during heavy fighting since Friday. Prime Minister Fouad Siniora described the group as a "terrorist gang", and said there would be no negotiation.

A militant spokesman said they would fight to "the last drop of blood".

"We will not surrender," vowed Fatah al-Islam spokesman Abu Salim Taha.

"The Nahr al-Bared camp will not fall despite the destructive shelling, and the army will not be able to enter," he told the AFP news agency.

Civilians in peril

However, there were suggestions that the army was advancing and had forced militants into the southern part of the camp, after fierce battles on the northern and eastern edges, BBC correspondent says.

But the reports could not be confirmed as the media were being kept at bay, she adds.

The army has said its forces have not entered the camp itself. There is a longstanding convention that the army does not enter Lebanon's 12 Palestinian refugee camps, leaving security inside to militant groups.

There is great concern for civilians in the camp, who have no access to power or medical help, BBC correspondent says.

Tens of thousands are thought to have fled the camp since fighting broke out on 20 May, but thousands reportedly remain.

Aid agencies have called for a ceasefire to allow more civilians to leave.

But the government and army are in no mood to end the siege now, BBC correspondent says.

The violence is the worst internal fighting Lebanon has seen since the end of its civil war 17 years ago.

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.

Photo caption

Buildings in Nahr el-Bared being shelled