Nahr al-Bared, Lebanon ? A little-known Islamic militant group based in a Palestinian refugee camp in northern Lebanon battled government troops Monday in some of the country’s fiercest fighting since the civil war ended in 1990, surprising the Lebanese military with the scope of the group’s weaponry and financing.

Tank and artillery fire pounded blocks of the Nahr al-Bared camp, creating towers of black smoke, as the second day of fighting pushed the death toll among soldiers and militants to at least 50. Palestinian officials told news agencies that nine civilians had been killed Monday inside the camp, but there was no word of Sunday’s civilian casualties.

The Lebanese army blocked the estimated 35,000 camp residents from leaving, apparently for fear that fighters would slip out. Hospital officials in the concrete-built towns immediately surrounding the camp said they were treating some wounded civilians but refused to let a reporter interview them, citing military orders.

The battle brought the previously obscure Fatah al-Islam group to prominence and underscored warnings that a growing number of militant groups are taking root in lawless places such as refugee camps and the battle zones of Iraq and Afghanistan. Fatah al-Islam, whose leader claims ties to al-Qaida, is thought to include 150 to 300 fighters of Palestinian, Lebanese and other origins.

Full-scale street battles broke out Sunday along a palm-lined and comparatively prosperous boulevard in the nearby city of Tripoli. Militants armed with machine guns and shoulder-fired missiles fought soldiers who attacked the group’s apartment hideouts with artillery, leaving whole buildings gutted. The two-day battle with the Sunni Muslim group opened an unwelcome second front for Lebanon’s weak military and its Western-backed government, which is already locked in a standoff with the Shiite Hezbollah movement. Worried Lebanese had been looking to the south, not the north, for trouble, fearing a resumption of last summer’s war between Israel and Hezbollah.

On Monday, two tanks perched on a cliff poured cannon fire into the refugee camp. Booming thuds marked rounds from artillery farther out in the surrounding hillside. The artillery fire appeared measured throughout the day, repeatedly hitting about four buildings on the outskirts of the camp.

Under a 1969 accord, Lebanese forces agreed not to set foot in the country’s 12 Palestinian refugee camps, and the army appeared to heed that restriction Sunday and Monday, sending munitions alone into Nahr al-Bared.

At dusk, the shelling redoubled. Flames broke out at spots across the camp, sending smoke wafting across the Mediterranean.

Fatah al-Islam gunmen fired at troops throughout the day. At times, gunmen and soldiers, separated by only a few dozen feet, faced off across a road bordering the camp. Families from surrounding towns fled along the same road, dodging gunfire.

Lebanese soldiers in armored vehicles lined up along the road served as both warriors and traffic police. When gunshots sounded from fighters hiding in the brush along the other side, military gunners held up a hand to hold back fleeing residents long enough for the soldiers to squeeze off several high-caliber rounds, then waved the civilian vehicles on.

At midday, Lebanese soldiers careened down the road in civilian cars, shouting warnings that militant fighters had broken out of the camp. “Go inside! Protect yourself!” soldiers shouted.

“Fatah al-Islam is coming!” small boys screamed as they ran along the road. Ambulances and U.N. vehicles with horns honking sped past them, retreating among scores of civilian vehicles.