The army used loudspeakers Friday to urge Islamic extremists inside a Palestinian refugee camp in northern Lebanon to surrender, as sporadic fighting continued, witnesses and security officials said.

The loudspeakers, which were set up on the roofs of some of the camp's collapsed buildings, were the latest military tactic to pressure Fatah Islam militants holed up inside the Nahr el-Bared camp to turn themselves in.

"We are getting closer and closer. You must surrender and you will have a fair trial," the military broadcast repeatedly overnight Thursday and Friday morning, according to the witnesses and security officials.

The officials, who spoke on customary condition of anonymity because they were not authorized to give press statements, said no members of Fatah Islam had responded to the calls.

The army has also set up security cameras to monitor the fighters' movements.

Sporadic fighting continued Friday as the army resumed shelling the remaining positions of the Al Queda-inspired militants.

Fatah Islam militants retaliated by firing four Katyusha rockets that landed in a village a few miles away from the camp, but there was no immediate word on casualties, according to the state-run National News Agency.

The militants have recently been firing the rockets on almost daily basis in what appears to be a new tactic to ease the army's pressure. A Lebanese teenager was killed and a young girl was injured Wednesday in rocket attacks on villages near the camp.

A Fatah Islam militant had warned they would send suicide bombers against the army if it continued its offensive against the besieged Nahr el-Bared camp located on the outskirts of the northern port city of Tripoli.

"We have hundreds of martyrdom seekers (suicide bombers) who were readied to go to Palestine but will instead blow themselves up against the Lebanese army if the battles continue," spokesman Abu Salim Taha warned in an interview published Thursday in a local newspaper.

Taha refused to say whether Fatah Islam leader Shaker al-Absi or his deputy, Abu Hureira, a Lebanese whose real name is Shehab al-Qaddour, had been killed in the fighting. He put the number of Fatah Islam dead at 50.

The whereabouts of Absi and Abu Hureira have been unknown since fighting began May 20.

The military has said 111 soldiers have been killed since fighting broke out in the camp two months ago.

The conflict with Fatah Islam militants is Lebanon's worst internal violence since the 1975-90 civil war. At least 60 militants and more than 20 civilians have been killed in the fighting, according to the Lebanese government and U.N. relief officials.