The liberal South Korean politician most likely to become the country's next president would, if elected, review how the government would deploy an advanced U.S. missile defense system and would consult China, two of his top advisers said on Friday, March 17, according to Reuters.

If Moon Jae-in, the front-runner for the May 9 presidential election, reverses policy on the deployment of the Terminal High Altitude Area Defense (THAAD) missile defense system, it will place him at odds with the United States, South Korea's biggest ally.

The conservative government of impeached president Park Geun-hye agreed to deploy the THAAD to guard against an attack by North Korea, but the decision sparked outrage in China, which responded with restrictions on some companies doing business with and in South Korea.

China says the system's radar can be used to spy into its territory.

Moon would likely "do a review of the validity of the decision", said Choi Jong Kun, a professor at Yongsei University and an adviser to Moon on foreign policy.

"While doing it he will consult with the United States, as well as China," Choi said in an interview with Reuters.

"At the end of the day, if the reality unfolds in a way that South Korea's national security and the economy were damaged because of the THAAD, not because of the North Korea issue, then it's not really a rational situation, is it?"

The comments are at variance with a tough stand taken by the new U.S. administration on North Korea.

U.S. Secretary of State Rex Tillerson, visiting Seoul for the first time since taking office, said on Friday a U.S. policy of "strategic patience" with North Korea has ended and military action would be "on the table" if North Korea elevated the threat level to warrant it.

Tillerson also said he expected the next South Korean government would "continue to be supportive" of the THAAD system.

China is South Korea's largest trading partner and the dispute over the missile system has left normally bustling shopping districts in the capital, Seoul, devoid of their usual crowds of Chinese tourists.

In China, the row has led to a freeze of South Korean television dramas and music, and product boycotts.