The June 28-30 gathering is seen as a crunch moment for the 30 North Atlantic Treaty Organization allies, four months into Russia's war in Ukraine.

Sweden and Finland, which have applied to join NATO, are sending delegations to the summit, and South Korea's new President Yoon Suk-yeol will also be the first leader from his country to attend.

Japan, a key US ally and not a NATO member, has delivered defensive supplies to Ukraine and imposed tough sanctions on Russia in tandem with the other Group of Seven countries.

"As the only Asian country in the G7, Japan's diplomatic capabilities are being tested," Kishida told reporters.

His attendance at the NATO summit will be "the first time for a Japanese prime minister", he said, adding that he intends to highlight the link between security concerns in Europe and Asia.

In recent weeks, Kishida hosted a summit of the Quad grouping and has made trips to countries including Singapore, where he gave a keynote speech at the Shangri-La Dialogue security summit on Friday.

"I myself have a strong sense of urgency that Ukraine today may be East Asia tomorrow," he warned there.