WASHINGTON — Vice President Mike Pence, dispatched to Asia to blunt a North Korean charm offensive at South Korea’s Olympic Games, said Wednesday that the United States planned to levy the toughest sanctions yet on the North over its nuclear and missile programs.

Mr. Pence’s threat, delivered in Tokyo, came two days after he had signaled openness to meeting with North Korean officials at the Games, somewhat muddying the harsh message he had been sent to project.

But in Japan, the vice president quickly reverted to form. Speaking alongside Prime Minister Shinzo Abe, Mr. Pence said he planned to “stand with our allies and remind the world that North Korea is the most tyrannical and oppressive regime on the planet.”

“We will continue to intensify our maximum pressure campaign until North Korea takes concrete steps toward complete, verifiable and irreversible denuclearization,” Mr. Pence said. He did not detail the precise timing or content of the sanctions. Analysts said they could target Chinese firms that do business with North Korea.