A woman carrying food bags walks past people queuing outside a state-run supermarket to buy essential food items in Colombo, Sri Lanka, on Sept. 3. AFP
UN agencies had estimated in June that 1.7 million out of the 22 million population in Sri Lanka required help.
The UN agencies in Colombo in a joint statement said they had raised $79 million to feed those in need, but the increasing number of poor people meant they needed an additional $70 million.
"Food insecurity in Sri Lanka has increased dramatically due to two consecutive seasons of poor harvests, foreign exchange shortages, and reduced household purchasing power," the statement said.
Sri Lanka is facing its worst economic crisis since independence from Britain in 1948 and has been enduring runaway inflation, power blackouts, and fuel rationing since last year.
The country defaulted on its $51 billion external debt in mid April and is in talks with the IMF for a $2.9 billion bailout.
Months of protests against high prices and shortages of food and medicines led to the toppling of president Gotabaya Rajapaksa in July.
The UN said its revised plan aims at feeding 2.1 million people, including pregnant mothers and school children and providing livelihood support to 1.5 million farmers and fishermen.
It also said that the poverty rate in the South Asian nation has doubled to 25.6 percent this year, up from 13.1 percent last year.