Republican presidential front-runner Donald Trump repeated his unfounded criticism of South Korea on Wednesday that the wealthy Asian nation relies on the U.S. for national defense without giving anything in return.

"I order thousands of televisions, they're all from South Korea. So we have 28,000 people on the border separating South Korea from this maniac in North Korea. We get nothing ... We get nothing. They're making a fortune. It's an economic behemoth," Trump said during a campaign speech in South Carolina.

Trump has repeatedly made such unfounded criticism, even though South Korea has shouldered part of the burden needed for the upkeep of 28,500 American troops stationed in South Korea to deter aggression from the communist North.

He made similar accusations against Japan.

"If somebody attacks Japan, we have to immediately go and start World War III, OK? If we get attacked, Japan doesn't have to help us. Somehow, that doesn't sound so fair. Does that sound good?" Trump said.

The billionaire real estate mogul also picked North Korea as one of the biggest problems facing the U.S.

"ISIS is a big problem, Russia's a problem, China's a problem.

We've got a lot of problems. By the way, the maniac in North Korea is a problem. He actually has nuclear weapons, right? That's a problem," he said, referring to North Korean leader Kim Jong-un.

Trump criticized Obama for focusing on global warming while facing such security threats.

"We've got a lot of problems. We've got a lot of problems.

That's right, we don't win anymore. He said we want to win. We don't win anymore. We're going to win a lot -- if I get elected, we're going to win a lot," he said.

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.

Seoul has long shared the cost of stationing U.S. forces.

Last year, the two countries renewed their cost-sharing agreement, known as the Special Measures Agreement, with Seoul agreeing to pay 920 billion won ($886 million) for the upkeep of the U.S. troops in 2014, a 5.8 percent increase from a year earlier.

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)