Nigeria's anti-corruption agency has launched a probe into allegations of fraud after a massive overpayment was made to a maritime organisation.
President Obasanjo says he is determined to stamp out corruption
More than $4m (£2.2m) was paid to the International Seabed Authority (ISA) in March for a bill of $22,000 (£12,000), according to the president's office.
The ISA, surprised by the amount, contacted the Nigerian Embassy in Jamaica, said the president's office.
Officials say an investigation has been launched into foreign ministry staff.
According to the statement, the probe would determine whether staff had deliberately inflated the debt in order to pocket the difference.
No details were given as to what the payments were for.
The Nigerian ambassador in Kingston, Jamaica, was "instructed to take possession of the money", and officials connected to the transfer of the monies were detained, the president's office said.
The ISA was set up through the UN to monitor maritime resources.
Nigerian President Olusegun Obasanjo has set up a special anti-corruption body, the Economic and Financial Crimes Commission, to fight fraud and corruption in a country ranked as one of the most corrupt in the world.