Kono said he made the offer during a meeting with Suh Hoon, the chief of South Korea's National Intelligence Service, in Tokyo.

Suh visited Tokyo to brief the Japanese leadership on the fast-moving diplomatic process that saw an announcement last week of a historic summit between North Korean leader Kim Jong Un and US President Donald Trump to discuss Pyongyang's denuclearisation.

Suh is scheduled to meet Prime Minister Shinzo Abe on Tuesday.

"If North Korea accepts inspections, Japan will fully cooperate in financial aid and other things so that the IAEA would be able to conduct inspections immediately," Kono told reporters.

"We have told the South Korean side about our stance," he added without elaborating.

Kyodo News reported on Sunday that Tokyo plans to cover most of the initial cost of 350 million yen ($3.3 million) to 400 million yen needed to finance inspections of the North Korean nuclear complex in Yongbyon.

Japan is also considering offering more help if the cost goes up, Kyodo said, quoting government officials.

The report could not be independently confirmed.

Japan and the United States see IAEA inspections as the first step toward the denuclearisation of the Korean Peninsula -- a key condition for their dialogue with Pyongyang.

The UN nuclear watchdog set up a specialist team last August to prepare for a potential restart of inspections, Kyodo said.