PANMUNJOM, Korea — U.S. Vice President Kamala Harris capped her four-day trip to Asia with a stop Thursday at the Demilitarized Zone dividing the Korean Peninsula as she emphasized the "ironclad" U.S. commitment to the security of its Asian allies in the face of an increasingly hostile North Korea.

The visit comes on the heels of North Korea's latest missile launches and amid concerns that the country may conduct a nuclear test. Visiting the DMZ has become something of a ritual for American leaders hoping to show their resolve to stand firm against aggression.

North Korea fired two short-range ballistic missiles on Wednesday, while Harris was in Japan, and fired one before she left Washington on Sunday. The launches contribute to a record level of missile testing this year that is intended to move North Korea closer to being acknowledged as a full-fledged nuclear power.

At the DMZ, Harris went to the top of a ridge, near guard towers and security cameras. She looked through bulky binoculars as a South Korean officer pointed out military installations on the southern side. Then an American officer pointed out some of the defenses along the military demarcation line, including barbed-wire fences and claymore mines. He said American soldiers regularly walk patrols along a path.

"It's so close," Harris said.

Harris then visited one of a row of blue buildings that straddle the demarcation line, where an American officer explained how the buildings are still used to conduct negotiations with North Korea. Sometimes they pass messages back and forth and sometimes they use a megaphone, he said.

"That's high tech," Harris joked, before adding, "We've stepped into history."

"It's still going," the colonel said.

Harris agreed. "The past and present are happening every day."

She then walked out of the building and up to the demarcation line. On the North Korean side, two figures dressed in what appeared to be hazmat suits peeked out from behind a curtain in a second-floor window. Then they disappeared back inside.

Harris described the North Korean missile launches as provocations meant to "destabilize the region" and said the United States and South Korea remain committed to the "complete denuclearization" of the North.

"I cannot state enough that commitment of the United States to the defense of the Republic of Korea is ironclad," she said.

"In the South, we see a thriving democracy. In the North, we see a brutal dictatorship," she said before flying out of the border on a U.S. military helicopter.

Earlier, Harris met with South Korean President Yoon Suk Yeol at his office in Seoul and reaffirmed the U.S. commitment to defend the South with a full range of its military capabilities in the event of war, Yoon's office said.

They expressed concern over North Korea's threats of nuclear conflict and pledged an unspecified stronger response to major North Korean provocations, including a nuclear test.

Harris and Yoon were also expected to discuss expanding economic and technology partnerships and repairing recently strained ties between South Korea and Japan to strengthen their trilateral cooperation with Washington in the region. Their meeting also touched on Taiwan, with both reaffirming their countries' support for "peace and stability" in the Taiwan Strait, according to Yoon's office, which didn't elaborate.

Harris' trip was organized so she could attend the state funeral of former Japanese Prime Minister Shinzo Abe, but her itinerary was dominated by security concerns, a reflection of fears about China's growing power and North Korea's ramped-up testing activity.

In every meeting, Harris tried to lay to rest any fears that the United States was wavering in its commitment to protect its allies, describing American partnerships with South Korea and Japan as the "linchpin" and "cornerstone" of its defense strategy in Asia.

Yoon, who took office earlier this year, had anchored his election campaign with vows to deepen Seoul's economic and security partnership with Washington to navigate challenges posed by the North Korean threat and address potential supply chain risks caused by the pandemic, the U.S.-China rivalry and Russia's war on Ukraine. But the alliance has been marked by tension recently.

South Koreans have decried a new law signed by President Joe Biden that prevents electric cars built outside of North America from being eligible for U.S. government subsidies, undermining the competitiveness of automakers like Seoul-based Hyundai.

During their meeting, Harris told Yoon that Washington will try to address South Korean concerns as the law is implemented, Yoon's office said.

Scott Snyder, an analyst at the Council on Foreign Relations, said the dispute over electric vehicles has swiftly become a firestorm that U.S. officials cannot ignore, although there may not be a simple solution.

"It's taking on a level of urgency that's making it into a political problem that requires management," Snyder said. "I don't know that it's going to be easy for the Biden administration to do that."

After meeting Yoon, Harris, the first woman to serve as U.S. vice president, held a roundtable with female leaders on gender equity issues.

Yoon has faced criticism for the lack of female representation in government and his downplaying of broader inequalities.

"If we want to strengthen democracy, we must pay attention to gender equity," said Harris, who also raised the issue with Yoon.

There are indications North Korea may up its weapons demonstrations soon as it attempts to pressure Washington to accept it as a nuclear power. South Korean officials said last week that they detected signs North Korea was preparing to test a ballistic missile system designed to be fired from submarines.

The U.S. aircraft carrier USS Ronald Reagan was to train with South Korean and Japanese warships in waters near the Korean Peninsula on Friday in the countries' first trilateral anti-submarine exercises since 2017 to counter North Korean submarine threats, South Korea's navy said Thursday.

U.S. and South Korean officials also say North Korea is possibly gearing up for its first nuclear test since 2017. That test could come after China holds its Communist Party convention the week of Oct. 16, but before the United States holds its midterm elections Nov. 8, according to Seoul's spy agency.

North Korea has punctuated its testing activity with repeated threats of nuclear conflict. Its rubber-stamp parliament this month authorized the preemptive use of nuclear weapons in a broad range of scenarios where its leadership comes under threat.

Nuclear diplomacy between the U.S. and North Korea remains stalled since 2019 over disagreements on easing crippling U.S.-led economic sanctions against the North in exchange for the North's disarmament steps.