US Secretary of Defense James Mattis (left) is welcomed by Japan’s Prime Minister Shinzo Abe ahead of their meeting at Abe’s official residence in Tokyo on June 29, 2018. AFP

TOKYO, Japan — US Defense Secretary James Mattis pledged Friday to maintain and strengthen the US security alliance with Japan amid fears that talks with North Korea could water down Washington’s longstanding security commitments in the region.

Mattis said the United States and its regional allies will maintain a “strong collaborative defensive stance” on North Korea, and that Japan will remain a “cornerstone” of regional stability.

In meetings with Japanese officials, Mattis sought to address Tokyo’s worries that its security interests could be left behind in President Donald Trump’s push to reach a denuclearization deal with North Korean leader Kim Jong Un.

“We’re in the midst of very unprecedented negotiations right now with North Korea, but in this dynamic time, the longstanding alliance between Japan and the US stands firm,” Mattis insisted next to his Japanese counterpart Itsunori Onodera.

“There is absolute reassurance between the two of us that we stand firm,” he pledged.

Regional allies were caught wrong-footed by Trump’s unexpected announcement on June 12 to suspend joint military exercises between the US and South Korea that had previously been seen as a vital measure to contain the North Korean threat.

Following the historic summit in Singapore between Trump and Kim, the US president said he wanted a halt to the drills, describing them as “expensive” and “provocative”. But US allies did not appear to be forewarned.

Mattis said the decision was taken “to create space for our diplomats to negotiate strongly and increase the prospect for a peaceful solution on the peninsula.”

“At the same time, we maintain a strong collaborative defensive stance, to ensure our diplomats continue to negotiate from a position of unquestioned strength,” he said.

Onodera said the drills were “important for the stability of the region,” but acknowledged that the decision to suspend them was valuable for diplomatic efforts to get Kim to give up his nuclear threat.

Japan and South Korea both feel a particular threat from Pyongyang’s proven short and medium range ballistic missiles and its possession of chemical and biological weapons.

North Korea, which has previously vowed to sink the Japan into the sea, fired two test missiles over the island nation last year, with others splashing into the sea nearby.

Tokyo and Seoul fear US negotiations will focus on the intercontinental ballistic missiles that North Korea showed last year could reach US territory and potentially deliver a nuclear warhead, rather than shorter-range missiles.