John Kerry, the US secretary of state, has said Washington is willing to engage with North Korea as long as it takes steps to give up nuclear weapons.
Kerry said during a meeting with Shinzo Abe, prime minister of Japan, that the on burden is on Pyongyang to follow "to observe laws and the norms of international behaviour".
"The burden is on Pyongyang," he said. "North Korea must take meaningful steps to show that it will honour commitments that it has already made".
At a separate meeting with Japanese students, Kerry also said that the US and Japan are united in addressing the North Korean crisis.
"One thing is certain, we are united. There can be no confusion on this point. The North's dangerous missile programme threatens not only North Korea's neighbours but it threatens its own people," he said.
Earlier in a meeting with his Japanese counterpart, Fumio Kishida, he stressed that Washington wanted to help ease the rising tensions in the region.
"I think it is really unfortunate that there has been so much focus and attention in the media and elsewhere on the
subject of war, when what we really ought to be talking about is the possibility of peace," Kerry said.
He said "denuclearisation" was a reality and that peaceful resolution to the issues of North Korea remained a "big priority".
The visit came as the North celebrates its biggest holiday of the year, the Day of the Sun, the birth date of state founder Kim Il-sung.
The day is an occasion for pomp and perhaps a military display.
The North's state media, one of the few ways of glimpsing what is happening in the reclusive country, has so far ignored Kerry's swing to China, South Korea and Japan.
North Korea has for weeks escalated threats of nuclear attacks on the US and South Korea, raising tensions on the Korean peninsula.
In Seoul earlier, Kerry had said North Korea would be making a "huge mistake" if it launched one of its medium-range missiles during the current standoff. Japan, separated by less than 1,000km of water and a frequent target of North Korea's anger, is in easy range.
Follow coverage of escalating threats in Northeast Asia
Kerry's agenda in Tokyo also included Japan's territorial disputes with China, and the future of U.S. bases in Japan.
He repeated that while Washington took no position about the ultimate sovereignty of tiny isles in the East China Sea claimed by both China and Japan, the United States "opposed any unilateral action that would somehow change the status quo".
A flare-up of the territorial row has raised fears of an unintended military incident near the islands, known as the Senkaku in Japan and the Diaoyu in China.
The US has said the islets fall under a US-Japan security pact, but is keen to avoid a clash in the economically vital region.