The raw ingredients of the ready-to-use therapeutic food (RUTF) have leaped in price amid the global food crisis sparked by the war and pandemic, UNICEF said.
Without further funding in the next six months, 600,000 more children may miss out on the essential treatment, which is a high-energy paste made of ingredients including peanuts, oil, sugar and added nutrients.
Alongside the wider pressure on food security, including climate change, the price rise could lead to "catastrophic" levels of severe malnutrition, the children's agency warned in a statement.
Severe wasting, when children are too thin for their height, affects 13.6 million children under 5 years old, and results in 1-in-5 deaths among this age group.
Even before the war and pandemic, 2-in-3 did not have access to the therapeutic food needed to save their lives, UNICEF said.