JUBA, South Sudan — Officials from a United Nations food agency airdropped 32 metric tons of food to refugees on the South Sudan-Sudan border, an expensive, last-ditch way to get food to tens of thousands of people who have been forced out of Sudan by fighting and hunger, an official said Thursday.

The food was wrapped in rugged bags and pushed out of a cargo plane that flew low and slow, then pointed its nose upward so the cargo slid out the rear, said Challiss McDonough, a World Food Program spokeswoman. No parachutes were used. The airdrop was used because a long rainy season has created muddy conditions, making ground deliveries slow and difficult for the refugees who have trekked to the camps.

“This is the first in a series of airdrops that aims to replenish rapidly diminishing food stocks for more than 100,000 people who have fled the fighting north of the border,” said Ertharin Cousin, director of the World Food Program.

The first airdrops were made Wednesday in Maban County in Upper Nile State. Camps there — along with another in a region called Yida — have received more than 160,000 refugees who have fled war on the other side of the border in Sudan.

The refugees in Maban come from the Nuba mountains in Sudan’s Blue Nile State. They have fled fighting between rebels in the north and Sudanese government forces. Fighting between the government and the rebels broke out in Sudan’s South Kordofan State after South Sudan’s independence in July 2011. The clashes spread to neighboring Blue Nile State.

The World Food Program plans to deliver up to 2,000 metric tons of food to Maban in the coming days and weeks.