TRIPOLI, Lebanon (AP) – Military aid began arriving Friday after America said it will rush supplies to the Lebanese army fighting Al Qaeda-inspired Islamic militants barricaded inside a Palestinian Arab refugee camp in the country’s north.

Meanwhile, sporadic gunfire exchanges early Friday punctured the lull in the fighting as the Lebanese army continued to build up around the Nahr el-Bared refugee camp near the port city of Tripoli.

The move appeared to be either a preparation to storm the camp – a maze of narrow streets and tightly packed residential buildings where hundreds of Fatah Islam militants are holed up – or a tightening of the siege to force them to surrender. Thousands of Palestinian refugees are also trapped inside.

A deputy Fatah Islam leader threatened more violence if the army attacks Nahr el-Bared. Abu Hureira told the pan-Arab Al Hayat daily by telephone that “sleeper cells” in other Palestinian camps and elsewhere in Lebanon were awaiting word for a “violent response.”

Although American officials said the military aid to Lebanon had been agreed to before the fighting broke out this week, the speedy shipment Friday marked the first tangible American backing of the Lebanese authorities in their fight with the militants.

Secretary of State Rice on Thursday renewed the Bush administration’s strong support of the Lebanese government.

“I certainly hope that the Lebanese government will be able to deal with these extremists,” Ms. Rice said. “It’s just another example of extremists in the Middle East who are trying to destabilize democratic governments.”

American military assistance was renewed after Syria withdrew troops from Lebanon in 2005, and increased after last year’s summer war between Lebanese Hezbollah militants and Israel.

Hoping that a boosted army could eventually disarm Hezbollah, the U.S. has pledged $40 million in military aid. Lebanon’s 70,000-strong army is underarmed and overstretched, with army leaders complaining of a lack of heavy armor, anti-aircraft missiles and the absence of an air force.

At the camp, gunfire had grown heavier Thursday shortly after nightfall and continued on and off through early Friday, as both sides probe each other’s defenses. Troops have entrenched their positions around the camp but did not appear to be attempting to advance. Reinforcements from other regions are also arriving, mostly drawn from elite commando units.

Two military transports landed at the Beirut airport Friday morning, spotted by many residents of the capital. The military refused to comment, apparently because of the sensitivity of the matter.

Security officials, speaking on condition of anonymity because they were not authorized to talk to the media, said that a United Arab Emirates air force plane had landed late Thursday with the first supplies.

A Pentagon official said Thursday that America would provide ammunition and other equipment to the Lebanese army in a military airlift of eight planes. An American military official said the Lebanese government had asked America to expedite a shipment of a broad range of equipment and ammunition already in the pipeline for delivery.

Lebanese officials subsequently told Washington they needed the ammunition right away, said the official, who spoke on condition of anonymity because of the sensitivity of the issue. All of the materials en route had previously been requested, the agreements were already in place, and they were in the delivery process, the official said.

The fighting in Lebanon, which erupted Sunday when police raided suspected Fatah Islam hideouts in Tripoli while searching for men wanted in a bank robbery, has killed some 50 combatants and many civilians.

Thousands of Palestinian civilians – mainly women and children – have fled the camp on the outskirts of this northern port city, but thousands still remain inside.

Amid the swell of international support, Prime Minister Fuad Saniora vowed to wipe out Fatah Islam. In a televised address Thursday, he said that Fatah Islam was “a terrorist organization … attempting to ride on the suffering and the struggle of the Palestinian people.”

“We will work to root out and strike at terrorism, but we will embrace and protect our brothers in the camps,” Saniora said, insisting Lebanon has no quarrel with the 400,000 Palestinian refugees living in the country.

Under a 1969 agreement, Lebanese military stays out of the camps that are run by the Palestinians.

But Abu Salim Taha, a spokesman for the militants, repeated late Thursday that Fatah Islam would never surrender or flee but “fight until the last moment, the last drop of blood and the last bullet.”

Storming the Nahr el-Bared camp – a densely built-up town of narrow streets on the Mediterranean coast – could mean rough urban fighting for Lebanese troops and further death and destruction for the civilians inside.

It also could spark unrest in Lebanon’s 11 other Palestinian refugee camps. Although Palestinian factions have dissociated themselves from Fatah Islam, refugees in other camps, which are rife with armed groups, are angry over army bombardments that have partially destroyed Nahr el-Bared.

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Associated Press writers Lolita C. Baldor in Washington and Sam F. Ghattas in Beirut contributed to this report.