The UN World Food Programme in Nepal has condemned an attack on one of its food aid trucks on a road in the western district of Dang.
Many Nepalese would suffer without WFP handouts
It says that the truck - carrying 12 tons of food - was set on fire by a mob in the attack on Wednesday.
It says that the attack will "severely impact" the ability of WFP to provide food to millions of needy people.
The truck was carrying a month's worth of food rations for more than 1,700 undernourished women and children.
WFP says that the driver was lucky to escape unhurt in the attack, which destroyed the lorry and its cargo.
"This is the first time since the signing of a peace accord that such an incident has occurred and it represents an escalation in insecurity," a WFP statement released on Friday said.
The statement made no mention as to who might have carried out the attack.
Nepal's former Maoist rebels signed a peace deal last November.
This year has seen outbreaks of violence in the Terai plains of Nepal involving the local Madheshi community.
"Our efforts to provide humanitarian food assistance to flood-affected population in the Terai (southern plains) of Nepal continue to face significant challenges and delays because of ongoing violence and strikes.
"The destruction of the truck is likely to further impede our ability to maintain the delivery of food aid across all of our programmes - threatening the lifeline for over 2.5 million needy people in Nepal."
The UN agency says that if it to continue providing humanitarian food relief, its staff must be provided "unhindered and safe passage by all parties and individuals".
"Further attacks against transporters carrying WFP food aid, staff or implementing partners may force us to suspend humanitarian food assistance in Nepal until the safe passage of WFP cargo and WFP staff is assured," the statement said.
More than 13,000 people were killed during a 10-year fight by Maoist rebels to establish a communist republic in Nepal. The civil war ended with a historic peace accord last November.
The fighting brought further poverty and misery to one of the poorest countries in the world.
Human rights groups regularly accused both the Maoists and the military of gross human rights abuses.