Ewan McGregor has warned "famine is looming" in South Sudan, putting tens of thousands of children at risk of starvation.
McGregor, who is UK ambassador for relief charity Unicef, said babies born into hope after the country achieved independence in 2011 were now facing desperate circumstances after months of bitter fighting.
Unicef has warned that parts of South Sudan could slip into famine as early as next month as it faces a triple emergency of famine, fighting and disease on the third anniversary of its independence.
Unicef has only raised a third of the £89 million the charity says it needs to help South Sudan's children.
McGregor said in the Unicef appeal:
In July 2011 babies were born into incredible hope in South Sudan, as the country declared independence and was celebrated as the world's newest nation.
Now, three years on, the outlook for these same children has taken a dramatic and desperate turn.
Famine is looming. Children are already dying every day of hunger and of diseases like cholera.
Unicef said more than half a million children have fled their homes since fighting began, with 250,000 under fives at risk of severe malnutrition.