An artillery shell explodes in the besieged Nahr el-Bared refugee camp near the city of Tripoli in northern Lebanon. The Lebanese army continued Saturday to battle Islamic militants barricaded in the Palestinian refugee camp.

Tripoli, Lebanon ? A missile-firing helicopter joined the Lebanese army offensive against al-Qaida-inspired militants on Saturday, the second day of a push against Islamic fighters vowing a fight to the death inside a Palestinian refugee camp.

Army tanks shelled militant hideouts in the Nahr el-Bared camp by this northern port city, blasting upper floors of buildings where the militants placed snipers.

A Lebanese air force helicopter fired two missiles and strafed militant positions in the first use of airpower since fighting began with the Fatah Islam group on May 20. 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 al-Qaida-inspired gunmen barricaded in the refugee camp.

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

Prime Minister Fuad Saniora said about 250 members of Fatah Islam were still inside the camp. He promised Palestinians who fled Nahr el-Bared that they will be able to return and the camp will be rebuilt.

The militants “have no choice but to surrender,” Saniora told Dubai-based Al-Arabiya television, adding that the government would “assure this group justice and a fair trial.”

Saniora and others believe the group is linked with Syrian military intelligence aimed at destabilizing Lebanon – a claim Syria denies.

There were signs that Palestinians trapped inside the camp were trying to squeeze the militants out.

Abu Jaber, an official of the Popular Front for the Liberation of Palestine – a key Palestinian guerrilla faction that has stayed out of the fighting – told Lebanese Broadcasting Corp. television that Palestinians were trying to “isolate” the militants by locking up houses and barricading camp neighborhoods to keep them out.

Abu Jaber said 17 people had been wounded in the camp and about 400 houses destroyed in shelling Saturday.

“We hope that the army realizes that the shells are falling on the heads of innocent people,” Jaber said by cellular phone from Nahr el-Bared.

Most of the camp’s 31,000 refugees fled to the nearby Beddawi camp earlier in the fighting, but at least 5,000 are believed still inside.