President Salva Kiir of South Sudan has accused officials of stealing at least $US4 billion from state resources.
He has written to 75 current and former senior government employees, asking for the unaccounted money to be returned.
Information minister Barnaba Benjamin told the BBC that about $US60 million had been returned since the letters were sent last month.
The new nation is desperately in need of funds after its oil production, which accounts for 98% of revenue, was shut down in an argument with Sudan.
In a letter dated 3 May and reportedly sent sometime in the last 10 days, President Kiir wrote:
"People in South Sudan are suffering and yet some government officials simply care about themselves.
"Most of these funds have been taken out of the country and deposited in foreign accounts. Some have purchased properties, often paid in cash."
The letter also offered an amnesty to anyone returning
South Sudan seceded from Sudan to form the world's newest nation last July. It is one of the least developed countries in Africa.