US President Donald Trump raised the topic of renegotiating a free trade deal with South Korea first before mentioning cooperation on the North Korean nuclear front in a recent phone conversation with Moon Jae-in, South Korea's new president, an informed official here said Saturday.

"President Trump, during the phone conversation, first delivered congratulatory remarks, then said the FTA should be renegotiated for the mutual interest of both countries," an official at Cheong Wa Dae, South Korea's presidential office, told Yonhap News Agency Saturday.

Moon and Trump spoke over the phone on Wednesday, vowing to maintain close cooperation in handling North Korea's nuclear threats. 

The official, who was next to Moon as he spoke with Trump, also said the US president mentioned the trade issue "in a light fashion, mentioning it on a principle level" and added that the "focus was on the North Korean nuclear issue."

Moon reportedly did not offer a particular reply to Trump's mentioning of renegotiating the trade deal. 

While the official said the focus of the talks was on the nuclear issue, it does, to a certain extent, hint on Trump's commitment to renegotiate the trade pact.

Trump called the free trade agreement with South Korea a "horrible deal" in a recent interview with the Economist, saying that Washington has already informed the Seoul government of its intention to renegotiate it.

But a government source well versed in US-South Korea matters said Seoul has not received any official indication from Washington of a renegotiation.

"We will counteract accordingly when we receive a request for renegotiation," the source said. Seoul is reportedly reviewing contingency scenarios in case a renegotiation actually takes place.

South Korea and the US enforced the FTA in 2012 after years of grueling negotiations. Experts here see it as mutually beneficial, though the US claims that it is "tilted" in favor of Seoul. (Yonhap)