The UK will give South Sudan and Somalia aid packages of £100 million each following famine warnings in the two war-torn states.
More than a million lives are hoped to be saved by the measures announced by the Government, which is to provide food, safe drinking water and emergency healthcare in regions worst affected by conflict and drought.
A state of famine has been declared in parts of South Sudan, where 100,000 people are said to be on the verge of starvation.
The UK must respond to the crises facing these countries to “avoid catastrophe”, said International Development Secretary Priti Patel in a statement.
“The world faces a series of unprecedented humanitarian crises and the real threat of famine in four countries. These crises are being driven by conflict and drought and we must respond accordingly,” she said.
“Our commitment to UK aid means that when people are at risk of dying from drought and disaster, we have the tools and expertise to avoid catastrophe.”
Severe drought in Somalia, where civil war has raged for more than two decades, resulted in the world’s last major food crisis in 2011.
Nearly 260,000 people died of hunger – half of them children under the age of five – according to a UN report.
DFID said that all the signs were pointing to a famine just as bad, or worse, in coming months.
Emergency food will be delivered to up to one million people in Somalia, where ongoing conflict has deprived more than six million of reliable access to food and 360,000 children are acutely malnourished.
Nutritional support will be provided to more than 600,000 starving children and pregnant and breastfeeding women.
Safe drinking water is also to be made available to a million people, and emergency healthcare for 1.7 million people.