Defense Secretary James Mattis focused on the nuclear threat from North Korea in his first overseas trip Thursday, sending a signal about U.S. defense priorities at the outset of the Trump administration.

Mattis began a lightning-fast visit to Asia this week — the first foreign trip by a member of President Trump’s still-incomplete Cabinet — less than two weeks after being sworn in as the Pentagon boss.

After touching down in Seoul, Mattis met with senior officials in the South Korean capital, including Hwang Kyo-ahn, the acting president. The retired Marine general’s visit takes place at a time of political upheaval in South Korea caused by a major political scandal as the Constitutional Court considers whether to uphold lawmakers’ vote to impeach President Park Geun-hye.

Speaking to reporters before his arrival, Mattis said he would use the talks in Seoul, and those later in the week in Tokyo, to solicit the views of South Korean and Japanese leaders about how best to mitigate the threat from Pyongyang. “Together we confront the North Korean situation,” he said of the two U.S. allies.

The visit is an indication of mounting worry about what Mattis described as unpredictable actions by North Korea. Kim Jong Un, North Korea’s young leader, suggested at the beginning of the year that his country would soon be ready to test an intercontinental ballistic missile (ICBM), making a strike on the United States possible.

North Korea’s secretive leadership has already conducted five nuclear tests — the most recent in September — stoking U.S. worries about the country’s offensive ability.

Patrick Cronin, a scholar at the Center for a New American Security, said that despite sanctions and dire poverty, North Korea was “on the cusp of being able to demonstrate and deploy all the sinews of a nuclear-weapon state.”

“Indeed, within the span of President Trump’s current four-year term in office, it is probable that Pyongyang will deploy a mobile, nuclear-tipped ICBM capable of striking U.S. territory,” he said.

Last month, then-Defense Secretary Ashton B. Carter said the United States would shoot down an ICBM from North Korea only if it posed a direct threat.

How the Trump administration will approach that prospect remains unclear. While Trump has tweeted North Korean development of a nuclear-capable missile able to strike U.S. soil “won’t happen,” he has also made isolationist comments and suggested that non-nuclear states should be able to acquire nuclear weapons.

Mattis declined to say what additional actions the U.S. might take in an attempt to rein in North Korea. He did say he would address deployment of the Terminal High Altitude Aerial Defense system, or THAAD, with Korean officials.

“If it were not for the provocative behavior of North Korea, we would have no need for THAAD out here,” Mattis said.

With South Korean elections on the horizon and China continuing to demonstrate its opposition to the defense system, the future of the THAAD is likewise uncertain.

A former head of U.S. Central Command, Mattis has spent much of his career focused on military issues in the Middle East, and said his first trip would seek to update him on the challenges in the Asia-Pacific region.

Mattis’ support for the U.S. alliance with South Korea and Japan will go some ways toward assuaging fears among Asian allies, rattled by political tumult in America and Trump’s questioning of U.S. military partnerships in the region. The president has also pulled out of a major trade deal with Asian allies.

The trip takes place amid broader tumult in U.S. foreign policy, as Trump and his advisers threaten Iran and deliver jolts to relationships with allies such as Mexico.