Philippine President Rodrigo Duterte plans to cancel his trip to Japan next month due to the ongoing crisis in the southern Philippine region of Mindanao, now under martial law, government sources said Sunday.

"(President) Duterte doesn't want to travel unless the situation in the country is stable," one of the sources said, referring to the fighting between Philippine army troops and Islamic extremists last week. Duterte imposed martial law on the entire Mindanao group of islands last Tuesday.

The source said travel orders issued to the president's staff were being revoked, meaning their trips to Japan are canceled.

But sources from the Department of Foreign Affairs declined to confirm the matter.

Duterte was invited to be one of the speakers at the International Conference on the Future of Asia on June 5-6 in Tokyo. The forum is sponsored by Nikkei Inc. and attended by Asian political and business leaders.

The president was also scheduled to hold talks with Prime Minister Shinzo Abe. It would have been his second visit to Japan since taking office in June last year.

Duterte declared martial law over the entire Mindanao area for 60 days, prompted by the occupation by the Islamic State-inspired Maute militant group of parts of the predominantly Muslim city of Marawi in Mindanao. He imposed the order while on a trip in Russia.

The president cut short his visit there to return home and deal with the crisis.

The death toll in the ongoing fighting has climbed to at least 61 militants, while no less than 15 soldiers and 19 civilians have also died.

Under the Philippine Constitution, the declaration of martial law empowers the government to conduct warrantless arrests, effectively tightening its hold over a lawless area or a region beset by rebellion during its duration.