Mozambique’s government has paid lawyers around 100m meticais ($1.6m; £1.2m) to try and keep the former finance minister from facing trial in the US, according to an anti-corruption organisation.
Manuel Chang has been detained in South Africa since December 2018 over bribery allegations.
The US is seeking to extradite him from South Africa for trial.
It is related to loans of nearly $2bn (£1.4bn) that Mr Chang signed in 2013 and 2014.
The money was used in part to buy hugely overvalued boats in what has become known as the tuna bond scandal.
Mr Chang denies any wrongdoing.
The Mozambique-based Centre of Public Integrity (CIP) published invoices which show Mozambique’s Attorney General's Office employed a South African law firm to fight for the extradition of Mr Chang back to Mozambique.
The CIP argues that Mr Chang should be extradited to the US.
It says those arguing for his extradition to Mozambique are motivated by a desire to stop more information on the hidden debts being exposed to the public.