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.

If Moon Jae-in, front-runner for the May 9 presidential election, reverses policy on the deployment of the Terminal High Altitude Area Defence (THAAD) 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 THAAD to guard against 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.