A former government minister in Nigeria stole $6bn (£3.8bn) of public money, a state governor has alleged.
Adams Oshiomhole said US officials informed President Muhammadu Buhari of the alleged theft during his visit to Washington last month.
Mr Buhari took office in May, ending the rule of the Peoples Democratic Party (PDP).
The PDP has repeatedly denied allegations of widespread corruption during its 16-year rule.
Mr Oshiomhole, who accompanied Mr Buhari to Washington, did not name the minister who allegedly stole the money.
During his visit to the US, Mr Buhari said he had asked the US to help recover $150bn "stolen in the past decade and held in foreign bank accounts".
US officials described the theft during the PDP's rule as "earth-quaking", Mr Oshiomhole, the Edo State governor, told journalists in the Nigerian capital, Abuja.
The PDP said Mr Buhari's visit to Washington was a failure, in particular for failing to obtain "any sort of tangible gain for the fight against terrorism".
Mr Buhari, a former military ruler, was invited to Washington shortly after becoming the first opposition candidate to win a national election in March.
He succeeded President Goodluck Jonathan.
Nigeria is Africa's biggest oil producer, but the majority of its citizens live in poverty. Its oil sector has often been hit by allegations of corruption.