The United States gains benefits from its military alliance with South Korea, such as selling arms to the Asian ally, an American expert said Friday, rejecting Republican presidential front-runner Donald Trump's claims that the U.S. provides defense to the South for free.

David Straub, a former State Department director for Korea and currently associate director for the Korean Studies Program at Stanford University, also said that South Korea is paying a sizable amount of money for the upkeep of the 28,500 American troops.

"South Korea pays quite a bit, about a billion dollars a year, I believe. That's a lot of money, and then the U.S. gets other benefits," Straub said in an interview with Yonhap News Agency. "We sell more arms to South Korea because of the relationship and so our arms industries make money and so forth."

Trump has repeatedly made unfounded criticism that South Korea is relying on the U.S. for defense against North Korea without paying anything in return.

Last year, the two countries renewed their cost-sharing agreement, with Seoul agreeing to pay 920 billion won (US$886 million) for the upkeep of the U.S. troops. 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.

Straub said Trump is trying to appeal to voters who feel that "the U.S. is the victim in its relationship with almost all the countries where it has militaries, including Korea."

Neither South Korea nor the U.S. are victims of the alliance, he said.

"I think he thinks by saying that the U.S. is losing money in its dealings with Korea, he will appeal to some Americans," the expert said. "That argument is ... not really Korea specific. He's using that as an example to the American people to say, 'Look, because we have weak leaders, everywhere in the world where we deal with foreigners we are victims.'" (Yonhap)