"If you analyze the trade gap and the situation with free trade agreements, you have maybe three categories, I would say. You have surpluses with Canada, Australia and Singapore. And then you have a bunch of countries where it kind of goes up and down, numbers aren't very large," Lighthizer said.

"And then you have Mexico and Korea, and those two are large, deficit countries," he said. "When I look at deficits, I try to ask myself what does it tell me about the rules of trade as they pertain to that country. Because our objective is not just to get the trade deficit down. Our objective is to get more efficiency in the market, is to get rid of trade barriers everywhere."

The USTR trade policy report, released on March 1, said that the Korea deal "coincided with a dramatic increase in our trade deficit" with the South, noting that the total value of US goods exported to South Korea fell by $1.2 billion, while US imports of goods from South Korea grew by more than $13 billion.

The report was seen as a strong indication that the US could seek a renegotiation of the pact.

During the campaign, Trump blamed free trade deals for job losses and other American economic problems in an attempt to woo voters struggling with economic difficulties. Since taking office, Trump also made protection of American workers and companies from foreign competitors his No. 1 priority.

After taking office, Trump withdrew the US from the 12-nation free trade deal Trans Pacific Partnership and has stepped up attacks on NAFTA, spurring concern that his next target could be the pact with Korea that he denounced as a job-killing deal during the campaign. (Yonhap)