U.S. National Security Adviser John Bolton has held talks with Japanese officials, presumably to discuss a U.S.-led military coalition to safeguard shipping in the Strait of Hormuz amid escalating tensions in the region.

Japan, whose use of force is limited to self-defense of itself and its allies under its pacifist constitution, is cautious about a military coalition.

Prime Minister Shinzo Abe says he wants to learn more about Washington's intentions before deciding if or how Japan can cooperate.

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Bolton, after meeting with Japanese Foreign Minister Taro Kono on Monday, said they "covered a lot of ground," but did not elaborate.

Japanese media said Bolton might also discuss an escalating spat between Japan and South Korea over trade and wartime labor issues.