"The drills and the US military stationed in South Korea play a vital role in East Asia's security," Japan's defence minister Itsunori Onodera said when asked about Trump's surprise announcement.

"I hope to share this recognition between Japan and the US, or among Japan, US and South Korea," he told reporters.

Trump stunned observers Tuesday, after meeting North Korea's leader, by saying the regular joint US-South Korea military exercises would be halted as Washington fleshes out a deal with Pyongyang.

"We will be stopping the war games, which will save us a tremendous amount of money, unless and until we see the future negotiation is not going along like it should," Trump said.

"Plus, I think it's very provocative," he added, saying further that "at some point" he wanted to withdraw US troops from the South, without suggesting a timeline.

Security experts warn that a reduction in US military presence in East Asia would alter the balance of power in the region as China's engages in a rapid military build-up.

Onodera said Japan's policy remained unchanged after the Trump-Kim summit.

"There is no change in our policy of putting pressure" on North Korea, he said, adding that Japan wanted concrete action from the North over its nuclear and missile ambitions, as well as on the issue of Japanese abducted by Pyongyang decades ago.