Joe Biden is currently on his first trip to Asia since taking office as president.
On Saturday, he visited the South Korean capital Seoul.
He began the visit by honoring soldiers who were killed while defending South Korea, many of them with American soldiers during the Korean War.
Biden also met with his South Korean counterpart, President Yoon Suk-Yeol.
The leaders wrote in a joint statement that they were open to expanding their joint military exercises, in response to the threat from North Korea.
During a press conference after the meeting, Yoon Suk-Yeol said that the common goal of the presidents is a total nuclear armament of North Korea.
Brief greeting
Before Biden left Seoul on Sunday, he was asked by a reporter about a greeting to North Korea's Kim Jong-Un.
The answer was concise and read: "Hello, period.".
It reports, among others, the news agency Reuters.
The president is also said to have said during his first trip to Asia that he is prepared for everything North Korea does and that he is not worried about the risks of a new weapons test while he is in the area, CNN reports.
Discuss possible alliances
During his visit to Japan, President Joe Biden will, among other things, meet with Japanese business leaders.
On Monday, talks with Emperor Naruhito and Prime Minister Fumio Kishida await.
According to the news agency TT, Biden will, among other things, discuss possible alliances with Japan's Prime Minister.
The White House's security adviser announced on Sunday that the United States plans to create a Pacific Pact with related countries to counter China's influence.