New Delhi, Sept. 19 -- At 14 months, Adut Duor should be walking. Instead, his spine juts through his skin and his legs dangle like sticks from his mother's lap in a South Sudan hospital. At half the size of a healthy baby his age, he is unable to walk.

Adut's mother, Ayan, couldn't breastfeed her fifth child, a struggle shared by the 1.1 million pregnant and lactating women who are malnourished in the east African country.

"If I had a blessed life and money to feed him, he would get better," Ayan said at a state hospital in Bor, 200 kilometers (124 miles) from the capital, Juba.

A recent U.N.-backed report projects that about 2.3 million children under 5 in South Sudan now require treatment for acute malnutrition, with over 700,000 of...