SEOUL - South Korean police said Thursday they had arrested three Nigerians for allegedly obtaining millions of dollars from Citibank with a forged document purportedly from Ethiopia's central bank.

Police said the suspects were caught Monday in the Yongsan district of Seoul following a tip-off from a local bank employee as they tried to withdraw money from a bank account. It had been frozen at Citibank's request.

In August the trio allegedly sent a forged payment request from the Ethiopian central bank to Citibank in New York.

"Citibank apparently transferred most of the money, including nine billion won (6.4 million dollars) sent to four local banks in Seoul," Detective Jung Hyun-Soo at Yongsan police station told AFP.

It was unclear whether money was withdrawn from accounts in other countries, he said.

Of the nine billion won transferred to South Korea, police said the Nigerians had already withdrawn eight billion and were detained while trying to obtain the remaining one billion.

Han Jeong, a senior police officer at Yongsan, told Yonhap news agency the Nigerians had already handed over most of the eight billion won to unspecified Ethiopians.

"After belatedly discovering that the documents had been forged, Citibank notified the Korean banks," Han said.

Two of the suspects were in South Korea on business visas while a third was an illegal immigrant. Their names were withheld.

"We're working closely with police in their investigation," a Citibank Korea spokeswoman said.

Police said Citibank officials told them that the forged document looked authentic and had the signatures of the central bank governor and directors.