Republican presidential front-runner Donald Trump should study more about the U.S. alliance with South Korea, the chairman of the Senate Foreign Relations Subcommittee on East Asia said Thursday, rejecting Trump's accusations that Seoul is getting a defense free-ride from the U.S.

"We have a great relationship that has been taken on -- a lot of it on the shoulders of the South Korean people, who are paying a tremendous amount for this security," Sen. Cory Gardner (R-CO) said in an interview with Yonhap News Agency.

"It's important to the U.S. that that remains in place. It's important that the security remains in place. It is certainly a mutually beneficial agreement that we are there to provide protection to a great ally. Donald Trump probably needs to look at it a little more," he said.

Through conversations with Gen. Curtis Scaparrotti, commander of U.S. Forces Korea, and his visit to South Korea last summer when joint exercises were under way, Gardner said he spent a lot of time talking about "how our security presence works with Korea."

Asked if he's willing to give Trump any advice, Gardner said, "I'm certainly willing to give him advice. I'm not sure if he's willing to take advice, as we've seen."

Trump has repeatedly made such unfounded criticism that South Korea pays almost nothing while relying on the U.S. for its defense against the North, even though Seoul has shouldered part of the burden needed for the upkeep of 28,500 American troops stationed in South Korea.

The presence of U.S. troops in South Korea is a legacy of the 1950-53 Korean War, which ended in a truce, not a peace treaty, leaving the divided peninsula still technically at war, and Seoul has long shared the cost of stationing U.S. forces.

In 2014, the two countries renewed their cost-sharing agreement, known as the Special Measures Agreement, with Seoul agreeing to pay 920 billion won for the upkeep of the U.S. troops per year, a 5.8 percent increase.

Moreover, the American military presence on the peninsula is seen as in line with U.S. national interests in a region marked by a rising China. (Yonhap)