Two Lebanese Red Cross workers have been killed outside a Palestinian refugee camp where troops are battling Islamist fighters, officials have said.
The pair were evacuating civilians when they were hit by either machine gun or shell fire from the Nahr al-Bared camp.
A Palestinian cleric, who had been trying to broker a truce, was wounded in the leg in a separate incident.
Earlier, the army fired artillery shells at militants from Fatah al-Islam entrenched in the camp near Tripoli.
At least 11 people were killed in clashes near the camp over the weekend.
Lebanese troops have been trying to crush the radical Islamist group since fighting first broke out in the camp on 20 May.
Some 3,000 civilians are still thought to be inside the camp, which contained an estimated 30,000 people before the violence began.
The fighting, which has left more than 120 people dead, is the worst internal strife in Lebanon since the end of its civil war 17 years ago.
'Total impasse'
The two Red Cross workers were evacuating some of the wounded civilians out of Nahr al-Bared when their vehicle was hit by fire from within the camp.
The state-run National News Agency named the workers as Boulos Maamari and Haitham Suleiman. A third Red Cross worker was critically injured, the agency said.
The pair were the first personnel from the humanitarian group to have been killed since the conflict began.
Correspondents say it is not immediately clear whether they had been targeted deliberately.
In a separate incident, a member of a Muslim clerics' delegation trying to broker a deal between Lebanon's government and Fatah al-Islam was injured.
Sheikh Mohammed al-Hajj was shot in the leg by a sniper after entering Nahr al-Bared to hold talks with the group.
"I'm alright," he told reporters at a hospital in Tripoli.
"The [peace] initiative will continue... to stop the bloodletting."
Earlier, the clerics had said there was a "total impasse" between the two parties.
"The international leaders of the al-Qaeda network have taken over... and the Fatah al-Islam members are refusing to give up," a spokesman said.
PHOTO CAPTION
A Lebanese RED Cross ambulance carries two dead out of Nahr al-Bared