UNRWA condemns violence after gunmen storm Palestinian refugee camp
Schools were evacuated and the camp's operations were suspended for one day after armed militants stormed the Bostan al-Qudes area, near four UNRWA schools.
It put children's lives "at considerable risk" and "shocked and frightened" refugees, said UNWRA spokesman Christopher Gunness.
"One armed person entered UNRWA schools without authorisation, contrary to the inviolability and neutrality of UN premises and instructed children to leave the schools," Gunness said. "The school buildings were clearly marked with a UN flag."
UNRWA students were able to evacuate the area without injury, despite live fire continuing while the children were leaving, Gunness added.
Schools were closed after the incident on December 5, and "repeated armed violence" and "increased risks on lives of civilians" forced UNWRA to suspend its operations on Wednesday.
Ain al-Hilweh, located southeast of the port city of Sidon, is home to some 120,000 refugees.
Gunness said: "UNRWA calls on all those involved to respect the rule of law, the sanctity of human life and the protection of Palestine refugees, particularly of children."
Last month construction work began on an isolation wall to surround Ain al-Hilweh following "security concerns".
The wall and watchtower forms part of an agreement between Palestinian factions and the authorities in Lebanon in attempt to contain recent confrontations between Palestinians inside the camp and the Lebanese army.
The army has only limited authority over the camp which has been effectively controlled by local Palestinian factions since the late 1960s.
It has led the camp to gain a reputation as a "zone of unlaw" where militants linked to Islamist factions are sheltering to evade detection.