Lebanon's defense minister issued an ultimatum Wednesday to Islamic militants barricaded in this Palestinian refugee camp to surrender or face a military onslaught, as the army reinforced its positions, raising fears of what could be a bloody showdown. Fighters from the al-Qaida-inspired Fatah Islam militant group vowed not to give up and to fight any Lebanese assault. 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 the thousands of civilians who remain inside. It could also have grave repercussions elsewhere across troubled Lebanon, sparking unrest among the country's estimated 400,000 Palestinians. Already some of the other refugee camps in Lebanon, which are rife with armed groups, are seething with anger at the fighting. But the military appeared determined to uproot Fatah Islam after three days of heavy bombardment of the camp, sparked by an attack by the militants on Lebanese troops on Sunday following a raid on its fighters in the nearby northern city of Tripoli. "Preparations are seriously underway to end the matter," Defense Minister Elias Murr said said in an interview with the Al-Arabiya television. "The army will not negotiate with a group of terrorists and criminals. Their fate is arrest, and if they resist the army, death." Around half of Nahr el-Bared's 31,000 residents have fled the camp since a halt in the fighting Tuesday night, with families streaming out carrying plastic bags full of clothes. They traveled on foot and in cars, clutching babies, past burned out shops and wrecked cars on streets strewn with broken glass, garbage and even dead rats. But thousands remained behind, either too ill to travel or unwilling to abandon their homes, and are now in danger of being caught in the crossfire. Occasional gunshots broke the quiet Tuesday night, witnesses said, but there was no fighting throughout the day Wednesday. In the afternoon, the army brought seven more armored carriers to its positions ringing the camp. But the troops did not move beyond the front line. Army officials in Beirut refused to comment on the reinforcements. The first indications of the death toll from the three-days of bombardment began to emerge. UN relief officials said the bodies of at least 20 civilians were retrieved from inside the camp during the halt in fighting. Murr said 30 Lebanese soldiers have been killed in the battle and put the death toll among militants at as many as 60, including fighters from Lebanon, Jordan, Syria and Saudi Arabia. But a top Fatah Islam leader said only 10 of his men have been killed. Fatah Islam said it was ready for a fight. A militant who said he was a deputy leader of the group said Fatah Islam was willing into enter a permanent cease-fire with the military if they are allowed to remain in the camp. But "if they enter, we are ready. They can try but they won't be able to. They will face a massacre," he told the Associated Press in a building in the camp, giving his pseudonym as Abu Hureira and speaking with a Lebanese Arabic accent. Just how many Fatah Islam are here is not clear, but Abu Hureira said they number more than 500. Lebanese military officials said Wednesday they found the body of a militant named Abu Madyan, who they said was the group's second-in-command and had been killed in fighting Monday.