Washington will soon unveil its "toughest sanctions ever" on North Korea, US Vice President Mike Pence said Wednesday, adding that the Pyongyang regime would not be allowed to "hijack" the upcoming Olympics.

Speaking in Japan before attending the opening ceremony of the Winter Games in South Korea, Pence pledged that Washington would "intensify its maximum pressure campaign" on the North, working with Tokyo.

"I'm announcing today that the United States will soon unveil the toughest and most aggressive round of economic sanctions on North Korea ever," he said, without giving further details.

Pence's three-day visit to Japan came as Washington seeks to bolster ties with its allies in the region and maintain pressure on the regime in Pyongyang despite a recent thaw on the peninsula.