A U.S. senator, considered a key foreign policy adviser for Republican presidential front-runner Donald Trump, has expressed negative views of the Korea-U.S. free trade agreement, saying the deal brought no benefits to the U.S.

Sen. Jeff Sessions (R-AL) made the remark during a Senate plenary meeting last week, arguing that the Trans Pacific Partnership (TPP), a free trade agreement among 12 Asia-Pacific nations awaiting congressional approval, will be bad for the U.S. just like the deal with Korea.

"We will look at how the Korean trade deal that I supported in 2011 came nowhere close to being beneficial to the United States,"

Sessions said, according to congressional records. "In 2011, when President Obama signed the deal, the President said that it would increase American exports by $10 billion to South Korea. I thought that was a good thing. It sounded pretty good, but their estimates were way off."

The model that experts used for the Korean deal is the same one used to study the TPP, he said.

"Did we increase exports by $10 billion each year to South Korea, as the model suggested? Well, their imports to us increased by $12 billion, and as of last year, we only increased our exports to Korea by less than a couple of hundred million dollars more than in 2011," the senator said.

"We didn't get any increase at all -- virtually none. They had a huge increase to us, and our trade deficit with our allies and friends in South Korea increased 280 percent. This is a serious matter," he said.

Sessions said that he's "firmly opposed" to the TPP, which he said would be "bad for our country."

"If it is such a good deal, why don't they bring it forward? Why don't we have a debate here while elections are on?" he said, accusing the administration of President Barack Obama of trying to slip through the agreement after the presidential election.

"Why wait until after, when things settle down a little bit, in the President's words, when people can't be held accountable by their constituents for the votes they cast or they think they may be able to slide away afterward?" he said.

The senator's opposition to the Korea-U.S. trade deal raises concern because his views are expected to have an impact on Trump, who has long argued that U.S. allies are not paying enough for American defense support and the U.S. should end their protection unless they agree to pay more. (Yonhap)