Officials from the US treasury department have visited South Korea to discuss alleged currency counterfeiting by North Korea.
Daniel Glaser is responsible for combating terrorist financing
They had already visited Hong Kong and Macau, the former Portuguese territory seen as a centre for what the US calls "North Korea's criminal activities".
The treasury department team was led by Daniel Glaser, the official responsible for combating terrorist financing.
He briefed the South Korean government on his investigation on Monday.
The US says the North is involved in counterfeiting US dollars, drug smuggling and the export of weapons of mass destruction.
But South Korea has been much more cautious, saying it has no direct evidence against its northern neighbour.
The South is anxious not to offend the North for fear of jeopardising its policy of reconciliation.
North Korea has reacted angrily to the American allegations.
It is refusing to return to six-party talks on its nuclear programme until Washington drops financial sanctions that were imposed last year.
The US targeted a bank in Macau which is alleged to have helped launder North Korean money.
It also took action against companies thought to be involved in the weapons business.