james mattis swearing in mike pence sot _00001328.jpg
PHOTO: CNN
james mattis swearing in mike pence sot _00001328.jpg
Now playing
01:03
James Mattis sworn in as defense secretary
This image was taken during the first drive of NASA's Perseverance rover on Mars on March 4, 2021. The team has spent the weeks since landing checking out the rover to prepare for surface operations.
PHOTO: JPL-Caltech/NASA
This image was taken during the first drive of NASA's Perseverance rover on Mars on March 4, 2021. The team has spent the weeks since landing checking out the rover to prepare for surface operations.
Now playing
02:17
NASA releases stunning new images from Mars
PHOTO: ABC's "Jimmy Kimmel Live!"
Now playing
02:09
Sacha Baron Cohen plays Covid vaccine dealer to the stars
PHOTO: CNN
Now playing
04:37
Keilar calls out Tucker Carlson's show: Partisan junk food
PHOTO: MyHeritage
Now playing
01:01
Watch old photos come to life using AI
PHOTO: CNN/Getty Images
Now playing
06:46
McEnany says she expected 'peaceful' rally on January 6. Keilar rolls the tape
Now playing
01:26
No, Tom Cruise isn't on TikTok. It's a deepfake
PHOTO: ABC's "Jimmy Kimmel Live
Now playing
02:02
Eddie Murphy, Arsenio Hall reunite in 'Coming 2 America'
PHOTO: Courtesy AirlingRatings.com
Now playing
03:06
Virgin Atlantic CEO: We support Covid vaccine passports
Now playing
01:19
Warren proposes wealth tax: 'It's time for them to pay a fair share'
Now playing
01:43
Marriott CEO: Vaccinations are 'the key' to travel recovery

Story highlights

US Defense Secretary heads to Asia on his first official trip

US and Korean Ministers agreed over phone call to strengthen existing defense alliance

(CNN) —  

Secretary of Defense Jim Mattis has reaffirmed the US’ commitment to defend South Korea “against the evolving North Korean threat”.

Mattis spoke with the South Korean Defense Minister Han Minkoo Tuesday ahead of his inaugural trip as secretary of defense to visit Japan and South Korea, the US’ closest Asian allies.

Han and Mattis expressed their commitment to proceed with the THAAD missile defense system deployment and the need for closer co-operation on policies on North Korea, according to a statement released by the South Korean Ministry of Defense.

The THAAD system is designed to take down incoming projectiles and has been cited as a way to potentially stop a nuclear attack from North Korea.

00:48 - Source: CNN
What is THAAD?

The visit comes after Donald Trump, when campaigning for the US presidency, caused concern in Asia by suggesting Seoul and Tokyo develop their own nuclear weapons. Trump also suggested the two countries either pay more for their own defense, or the US provide them with less security support.

00:38 - Source: CNN
North Korea: The biggest issue for the next US president?

Amid heightened tensions

The phone call between Mattis and Han comes amid analysis of new satellite imagery that suggests North Korea is restarting a plutonium reactor.

Tensions are already high on the Korean Peninsula after North Korean leader Kim Jong-Un said his country was close to testing an intercontinental ballistic missile (ICBM) – the type of projectile that would be used to deliver a nuclear warhead – in a televised New Year’s Day address.

In the speech, Kim referred to North Korea as a “nuclear and military power in the east” and warned the US and its “vassal forces to stop nuclear threat and blackmail,” according to state news agency KCNA.

In 2016 North Korea backed up its fiery rhetoric with two nuclear tests – the country had only conducted three before in 2006, 2009 and 2013 – and a handful of land and sea-based missile tests.

China trying to stop THAAD

China is concerned about THAAD at the strategic level, analysts suggest, with the country viewing the defense system as part of a broader US strategy to extend its military alliance network from Japan all the way down to the South China Sea.

“The Chinese see THAAD as part of a containment network that’s not directed at North Korea, but them,” John Delury, associate professor of international studies at Yonsei University in Seoul, told CNN.

Beijing is doing “everything in its power to prevent the deployment of the defense system,” Delury added, including punitive measures on South Korean celebrities and companies.

Earlier in January, local Korean media reports suggested that everything from cosmetics to K-Pop stars had been hit hard by the South Korea-US alliance over THAAD.

When asked whether the cancellation of a concert by Korean musicians Sumi Jo and Kwun-woo Paik was owing to THAAD, during a press conference in January, Chinese government spokeswoman, Hua Chunying denied the claims.

But Kim Hankwon, a national diplomatic academy professor in South Korea, told CNN that it was likely that the import ban on certain Korean products and cultural exports was related to THAAD.

He said that in the long term, however, China would avoid going overboard with their warning messages.

“If China implements stronger punitive measures towards South Korea, South Koreans will look more towards the US and show hostility to China,” said Hankwon.

CNN’s Stella Ko in Seoul, Michael Callahan in Washington DC and Serenitie Wang in Beijing contributed to this report