The director of the UN's World Food Programme has said it is considering plans to ration food aid because of rising prices and a shortage of funds.
The WFP's budget requirements are rising by millions of dollars a week
Josette Sheeran told the BBC that the WFP needed increased contributions from donors to make sure it could meet the needs of those who already rely on it.
She said it also faced growing demands from countries like Afghanistan, where people were now unable to afford food.
Food prices rose 40% last year because of rising demand and other factors.
Earlier this month, the UN Food and Agriculture Organisation (FAO) said the rising price of cereals such as wheat and maize had become a "major global concern".
The FAO estimated poor countries would see their cereal import bill rise by more than a third this year. Africa as a whole is expected to see a 49% increase.
The organisation has called for urgent action to provide farmers in poor countries with improved access to seeds and fertiliser to increase crop production.
In an interview with the BBC on Monday, Ms Sheeran said the WFP was holding talks with experts to decide whether food aid would need to be stopped or rationed if new donations did not arrive at the agency in the short term.
The former US undersecretary of state said she hoped the cuts could be avoided, but warned that the agency's budget requirements were rising by several millions of dollars a week because of the higher food prices.
"If food is twice as expensive, we can bring half as much in for the same price and the same contribution," she said.
"It will take increased contributions to make sure we can meet those already assessed needs."
Ms Sheeran said there was an urgent need for the funding shortage to be addressed because "in many places, we are the only source of food for some people".
"We're also seeing some new growing needs in some places like Afghanistan, where people are being thrown into food insecurity just simply due to the higher food prices."
She said those who had been hardest hit so far were people in developing countries who were living on 50 US cents (£0.25) a day, 80-90% of which was already being spent on food.
Global wheat prices have risen 83% in the past year
"In some of these developing countries, prices have gone up 80% for staple food," she added. "When you see those kinds of increases, they are simply priced out of the food markets."
Even middle-class, urban people in countries such as Indonesia, Yemen and Mexico were increasingly being priced out of the food market or forced to sacrifice education and healthcare, she warned.
Ms Sheeran said Egypt had just widened its food rationing system after two decades and Pakistan had reintroduced ration cards after many years.
China and Russia were meanwhile imposing price controls, while Argentina and Vietnam were enforcing foreign sales taxes or export bans, she said.
The WFP's ability to mitigate the impact of rising food prices has also been hampered by a significant decrease in the past five years of supplies of "in-kind food aid" - food produced abroad and delivered to vulnerable people in emergencies.
In-kind food aid peaked in 2000, when there were large surpluses and low prices for cereals.
The US, the world's largest donor of food aid, has since reduced its surplus and instead chosen to provide funding to international agencies.