SEOUL - South Korean police said Tuesday they have seized almost 10,000 fake 100-US dollar bills, known as "supernotes" for their high quality, and arrested four people.

The Busan Metropolitan Police Agency said its arrest Monday of the four men led to the seizure of 9,904 100-dollar notes brought in from China.

They were caught trying to sell the notes for 50 dollars each in the southern port of Busan.

Police said they are still hunting a ethnic Korean Chinese citizen who was in charge of smuggling the fake bills from China. They said the "supernotes" were so skilfully made that counterfeit detection machines in local banks did not pick them up.

Police said they were cooperating with Interpol to determine the original manufacturers of the bogus bills and crack down on the operation.