Human Rights Watch says Angola's government must account for $32 billion missing from State coffers.
The New York-based organisation says that money should be benefiting the people of the oil-rich southern African state, who mostly live in poverty.
The rights group said Wednesday the missing money was identified by the International Monetary Fund in a December report and is believed to be linked to the state oil company Sonangol.
It includes $7.1 billion transferred into escrow accounts overseas and $24.9 billion that appear as "an unexplained discrepancy in government accounts."
The IMF said the money disappeared between 2007 and 2010.
The rights group previously identified more than $4 billion in oil revenues that went missing from Angolan government accounts between 1997 and 2002.