A large convoy of trucks carrying aid was “violently looted” in the Gaza Strip over the weekend and its drivers forced at gunpoint to unload supplies, the main United Nations agency that helps Palestinians said on Monday, calling it one of the worst such incidents of the war.

The agency said that the incident highlighted the “challenges of bringing aid into southern and central Gaza” despite months of attempts by aid agencies to help it arrive safely, and despite the urgency of the need. Earlier this month, a U.N.-backed panel said that all of Gaza faced a risk of famine between now and April, with the north at particular risk.

In much of Gaza, there are no police officers to prevent chaos as organized crime groups fill the vacuum. Their affiliations — whether to Gazan clans or armed groups like Hamas — are unclear.