Souleymane Ndene Ndiaye denied the gift amounted to corruption
Senegal has confirmed it gave money to an International Monetary Fund (IMF) official earlier this month, after previously denying the allegations.
Alex Segura was given almost $200,000 (£122,000) at the end of his three-year posting - money which the IMF says was paid back as quickly as it could be.
Prime Minister Souleymane Ndene Ndiaye said it was a goodbye present - part of an African tradition.
But opposition activists have condemned what they regard as a corrupt payment.
The fund said in a statement Mr Segura was given the present after a dinner with President Abdoulaye Wade, but did not realise the gift was money until he was about to leave the country for Barcelona.
"With Mr Segura worried about missing his flight, and concerned that there was no place to leave the money safely in Senegal, he decided to take the money aboard the plane," Reuters quoted the IMF as saying.
The cash was handed over to Senegal's ambassador in Spain.
The BBC's Hamadou Tidiane Sy, in Dakar, says the affair has sparked anger and outrage in Senegal.
He says Senegalese want to know why an IMF official was allowed to leave the country with so much money, and they also want to see whether anyone will be punished.
Anti-corruption campaigner Mamadou Mbodj said the case should be referred to the country's High Court of Justice.
"It is unacceptable in a poor country like ours to use the taxpayers' money to reward international civil servants who are already highly paid for their jobs", he told the BBC.
Aissata Tall Sall, spokeswoman for the Socialist Party, said the government had "exposed its true nature to the rest of the world".
She called for international sanctions and said it was unacceptable for the IMF and government to consider the issue closed.
The president has not commented on the affair, but Mr Ndiaye admitted the gift was given, while denying corruption.
"We in Africa have a tradition - when someone visits you, you give him a gift at departure," he told local media.