Plumes of white and gray smoke rose from the Nahr el-Bared camp as the army bombarded Fatah Islam militants with heavy artillery shelling. The militants appeared to be retreating deeper inside the camp, but one of their leaders vowed the group would not surrender.

Tanks and artillery pounded Fatah Islam positions on the northern edge of Nahr el-Bared, located on the outskirts of this northern Lebanese port city, in a wide area concentrated around 10 buildings.

According to an Associated Press photographer near the camp, a Fatah Islam sniper could be seen moving from one destroyed building to another, as Lebanese troops bombarded the damaged structures from where he was shooting.

Lebanese security officials said a Fatah Islam militant was firing rocket-propelled grenades at army positions from the minaret of a mosque. It was not clear if the army was going to strike the minaret.

The Lebanese government has demanded the group surrender, saying it's the only way to end the attack. But Abu Hureira, Fatah Islam's deputy commander, rejected the government calls.

"This is not only impossible, this is unthinkable. Our blood is cheaper than handing over our weapons and surrendering," said Abu Hureira, a Lebanese whose real name is Shehab al-Qaddour, in a telephone interview with the AP.

The refusal to surrender came as militants said one of their top leaders had been killed in the fighting.

The Fatah Islam leader killed, Naim Deeb Ghali, who is also known as Abu Riad, was the third-in-command of the group, Lebanese security officials said.

Abu Hureira confirmed that Ghali was killed Friday, but would not say whether he was a senior Fatah Islam official, referring to him only as "a brother."

Sunday's army artillery fire appeared directed at militant positions deep inside the camp, indicating the military was advancing further inside.

There was no way to tell exactly how deep the army had advanced, because the area had been sealed off and journalists were kept away.

But as part of the intensifying assault, the army on Saturday added air power to the battle. A helicopter gunship was deployed for the first time since fighting began May 20, firing two missiles and strafing militant positions. The air attack was an apparent attempt to block an escape route to the Mediterranean Sea.

Four soldiers were killed and 10 wounded Saturday in the offensive aimed at uprooting the militant gunmen barricaded inside the camp on the outskirts of this Lebanese port city. Abu Hureira said six militants have been wounded since the offensive began Friday.

The casualties raised the army's deaths to 38 in two weeks. At least 20 civilians and about 60 militants have been killed, but casualties in the camp in the last two days were unknown because relief organizations were banned from entering.

In other the developments, the main road linking Tripoli with the province of Akkar and the Syrian border reopened Sunday for the first time since Friday. Vehicles were seen passing on the road that was closed for two days by Lebanese troops over fears of snipers.