Adding to the anxiety, the United States cancelled another military exercise with South Korea scheduled for next month, Seoul said on Monday, after Washington cited constraints on U.S. forces due to the Iran war.
Trump has been frustrated by the failure of U.S. allies to support the war and made it clear that many of them must spend more on their own defence, a White House official said when asked about such concerns.
He is eager to restart talks with North Korea and secure a win on the international stage to counter his unpopular conflict with Iran, according to a person briefed on discussions between U.S. and South Korean officials.
Trump's push to meet Kim - which has so far drawn a frosty response from Pyongyang - could backfire and embolden nuclear-armed North Korea, said Itsunori Onodera, an influential Japanese lawmaker and former defence minister.
Such a prospect is "extremely troubling" for Tokyo, he said on a Fuji TV news programme last Thursday. Despite Trump's overtures, Pyongyang fired a volley of ballistic missiles off its east coast earlier that day, triggering alerts in neighbouring South Korea and Japan.
What worries Japanese officials more is Trump's approach as Tokyo embarks on talks with Washington over how much it should pay towards the cost of hosting U.S. forces, America's largest overseas deployment.
Japan is bracing for the possibility that Trump could, with little warning, demand a sharp hike that would be politically difficult to swallow, said a senior Japanese government official, requesting anonymity due to the sensitivity of the matter.
Trump could also wield upcoming U.S. military exercises with Japan in October as leverage, analysts say. Officials in Washington and Tokyo said they did not expect the exercises to be curtailed, though Trump could change his mind at any point, they cautioned.
The drills, known as Keen Sword, may already be smaller than their 2024 iteration because of the diversion of U.S. assets and personnel to the conflict with Iran.
That shift - which recently saw America's only forward-deployed aircraft carrier in Asia, the USS George Washington, depart for the Middle East to relieve the beleaguered USS Abraham Lincoln - has stirred concern that U.S. deterrence against China is being eroded.
During a visit to Asia this month, Pentagon policy chief Elbridge Colby said working with allies to ensure combat readiness along the so-called first island chain that runs from Japan through the Philippines is a priority for Washington.
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