BEIRUT, Lebanon (CNN) — Two Red Cross workers were killed Monday at a Palestinian refugee camp in northern Lebanon as Lebanese forces and Islamic militants battled, a Red Cross representative said.The two were killed when a militant group’s mortar shell struck their vehicle, Lebanese security officials told The Associated Press. On Sunday, heavy clashes with militants who are said to have ties to al Qaeda left six Lebanese soldiers dead. Fifty-nine Lebanese troops have been killed since the fighting began at the Nahr el-Bared camp more than three weeks ago, according to the Lebanese military.

The Red Cross has been trying to get non-combatants out of the camp since the fighting began. Between 3,000 and 5,000 civilians remain in the camp, relief officials told The Daily Star newspaper in Beirut. A Red Cross official told the newspaper evacuations were blocked. "Many people want to leave, but it has been difficult to reach them because of the debris and the unexploded ordnance on the streets," The Daily Star quoted Red Cross spokeswoman Virginia de la Guardia as saying.

Lebanese troops pushed deep inside the refugee camp on Friday and were reported to be about 80 meters (87 yards) from the militants, who were holding a key position inside the camp.

Islamist leaders have failed to persuade the leaders of the militant group, Fatah al-Islam, to surrender their weapons. Meanwhile, the military’s top commanders have insisted the militants will be crushed if they continue to resist.

The violence began May 20, when Lebanese internal security forces were conducting raids in a Tripoli neighborhood, triggering clashes near the refugee camp. Army sources said militants from Fatah al-Islam fired on the forces, who then returned fire.

The battles are the worst internal violence since the end of Lebanon’s civil war in 1990.

CNN’s Nada Husseini and Brent Sadler contributed to this report.