WASHINGTON — 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.

During a planned visit to Tokyo on June 3 and 4, Shanahan and Japanese Defense Minister Takeshi Iwaya are expected to focus on measures to strengthen defense cooperation in outer space, cyberspace and electronic warfare in response to China and Russia’s efforts to boost their respective capabilities, the sources said.

Iwaya and Shanahan are also likely to discuss recent short-range missile launches by North Korea and the denuclearization of Pyongyang.

Shanahan may meet with Japanese Prime Minister Shinzo Abe, as well.

The Pentagon chief is considering visiting Seoul on June 2-3 after attending an Asian defense forum slated for May 31 to June 2 in Singapore, according to the sources.

Tensions have been running high between Japan and South Korea since a South Korean destroyer allegedly locked its fire-control radar on a Japanese patrol plane last December, in addition to friction over long-standing wartime issues.

During the planned trip to Seoul, Shanahan and South Korean Defense Minister Jeong Kyeong Doo are expected to discuss bilateral defense cooperation, including how to run joint military exercises going forward, as the Trump administration continues denuclearization negotiations with North Korea.

In his address at the Singapore gathering, known as the Shangri-La Dialogue, on June 1, Shanahan is likely to spell out how the Pentagon will play a part in operationalizing the administration’s strategy of a free and open Indo-Pacific, according to organizers.

Shanahan has been acting defense secretary since January after Jim Mattis stepped down in December over policy differences with Trump.

Shanahan became deputy defense secretary in July 2017 after serving as senior vice president for supply chain and operations at Boeing Co.