OSAN, South Korea--U.S. President Donald Trump arrived in South Korea on Tuesday, the closest he has come to the frontlines of the nuclear standoff with North Korea, on a visit that could further aggravate tensions with Pyongyang.

Landing at Osan Air Base outside the capital Seoul, Trump stepped down from Air Force One onto a red carpet as he began his 24-hour state visit with a ceremonial military honor guard arrayed on the airport tarmac.

The White House says Trump’s trip is intended to demonstrate U.S. resolve over his hard-line approach to North Korean nuclear and missile threats, but many in the region fear that further bellicose presidential rhetoric could increase the risk of a devastating military conflict on the Korean Peninsula.

Three U.S. aircraft carrier strike groups will conduct exercises together in the Western Pacific in the coming days in a show of force rarely seen in the region, U.S. officials said, as Trump continues his 12-day Asia tour aimed at forging a united front against North Korea and developing trade.

Pyongyang’s recent nuclear and missile tests in defiance of U.N. resolutions and an exchange of bellicose insults between Trump and North Korean leader Kim Jong Un have raised the stakes in the most critical international challenge of Trump’s presidency.

On the second leg of his five-nation trip, Trump on Tuesday was due to tour the main garrison for U.S. troops stationed in South Korea, the sprawling Camp Humphreys, which lies about 100 kilometers from the border with reclusive North Korea. He will later hold talks with South Korean President Moon Jae-in.

Trump is seeking to further ratchet up pressure on Pyongyang following his visit to Tokyo, where he declared that Japan would shoot North Korean missiles “out of the sky” if it bought the U.S. weaponry needed to do so, suggesting that the Japanese government take a stance it has avoided until now.

The South Korea leg of Trump’s trip is an effort to present a united front despite differences with Moon over how to confront North Korea, as well as Trump's complaints over the two countries' trade agreement and South Korean defense spending.

Trump has rattled some U.S. allies with his vow to “totally destroy” North Korea if it threatens the United States, for deriding Kim as a “Rocket Man on a suicide mission” and for dismissing as pointless any diplomatic engagement with Pyongyang.

Kim, who has also made clear he has little interest in negotiations, at least until North Korea develops a nuclear-tipped missile capable of hitting the United States, has called Trump a “mentally deranged U.S. dotard.”