U.S. Defense Secretary James Mattis (right) arrives at Osan Air Base in Osan, South Korea, Feb. 2, 2017.
Mr. Mattis described his trip, the first overseas visit for any cabinet secretary under Mr. Trump's new administration, as a listening tour.
The commitment was made after Mattis met South Korea's acting president and prime minister, Hwang Kyo-ahn, in Seoul.
After campaign threats of possibly drawing down military support for South Korea, Trump may be trying to soothe hurt feelings by sending Mattis to Seoul.
Mattis declined to say what additional actions the USA might take in an attempt to rein in North Korea.
The visit comes amid increasing threats from North Korea that it is ready to test-fire a new intercontinental ballistic missile at any time.
South Korea and the United States say the deployment of THAAD is created to protect against North Korea's growing nuclear and ballistic capabilities.
"It's a priority for the President Trump's administration", Mattis told reporters en route to Seoul "We pay attention to the Northwest Pacific, to our two strong allies".
Together, they discussed several important issues, including the recent threats from Pyongyang, which declared itself close to testing an intercontinental ballistic missile capable of reaching the United States territory, according to the military officials.
Cui Zhiying, Director of the Korean Peninsula Research Centre at Tongji University, said that while Mattis had put the emphasis on the threats from North Korea during his trip to Seoul, Washington's real target was China. He did say he would address deployment of the Terminal High Altitude Aerial Defense system, or THAAD, with Korean officials.
In addition, the two defense ministers agreed to deploy the U.S. THAAD missile defense shield this year as planned, over objections from China and despite mounting opposition in South Korea. -South Korea alliance of more than 60 years "remains even more relevant today" and that the United States was "determined to take steps to strengthen the alliance further to defend against the evolving North Korean threat", according to a statement issued by the Pentagon.
"Strategies are games of give and take and I have to see their (South Korea's) view of it", Mattis said.
Trump hasn't said much about North Korea since.
Yet on Tuesday, just days ahead of Mattis's trip, Trump told leaders from the pharmaceutical industry that Japan was intentionally devaluing its currency and engaging in "global freeloading". "America is here to stay, contrary to what candidate Trump said during the presidential election previous year".
Kim Jong Un's regime carried out its last ballistic missile test on October 20, soon after USA and ally South Korea agreed to push further military and diplomatic measures to counter the Pyongyang's nuclear capabilities.
The Secretary of Defense then headed to the U.S. Force Korea (USFK) headquarters in Yongsan and received a briefing from Gen. Vincent K. Brooks, Commander at USFK.
The North appears to have also restarted operation of a reactor at its main Yongbyon nuclear facility that produces plutonium that can be used for its nuclear weapons program, according to a us think-tank, 38 North.
Mattis is scheduled to meet with South Korean defense minister Han Min-koo.
South Korea's president Park was impeached in December over a graft scandal.
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