Acting U.S. Defense Secretary Patrick Shanahan plans to travel to Japan in early June, making his first visit to the country since taking up the post in January, sources familiar with the plan said Tuesday.

Shanahan, whom President Donald Trump intends to nominate as his defense secretary, is also considering visiting South Korea prior to arriving in Japan, the sources said.

With the planned visits to the two U.S. allies, the Trump administration is apparently aiming to strengthen trilateral security cooperation at a time when Tokyo and Seoul are finding it difficult to mend ties soured over historical disputes and recent incidents.