TOKYO — US President Donald Trump expects that Japan's military will reinforce US forces throughout Asia and elsewhere, he said on Tuesday, as the key US ally upgrades the ability of its forces to operate further from its shores.

Trump's comments followed his inspection of Japan's largest warship, the Kaga, a helicopter carrier designed to carry submarine-hunting helicopters to distant waters.

The vessel, which will soon be upgraded to handle F-35B short take-off and vertical landing (STOVL) jets, sailed to India on a flag-flying mission last year, going through the contested South China Sea, much of which is claimed by Beijing.

"With this extraordinary new equipment the Kaga will help our nations defend against a range of complex threats in the region and far beyond," Trump said in a speech on the ship's hangar deck.

The refit of the vessel, and its sister ship, the Izumo, is expected to bolster US.forces operating from Japan by providing a refueling platform for US Marine F-35Bs.

Japanese Prime Minister Shinzo Abe, who accompanied Trump on the visit to the Kaga, has boosted defense spending since taking office in December 2012, stretching the pacifist constitution to ease limits on troop activities abroad.

He also wants to revise the post-World War Two charter to recognize the existence of Japan's military.

The Kaga and the Izumo are the biggest aircraft carriers Japan has operated since its wartime defeat, but its Self Defense Forces designate them as destroyers, as constitutional curbs forbid possession of weapons that could be used to attack other countries. — Reuters