Trump told the cable television network: "We get paid nothing, we get paid peanuts" for deploying the troops to South Korea. But Seoul, still technically at war with North Korea, has shouldered part of Washington's cost for stationing its troops in the country since 1991.
Under a five-year cost-sharing accord reached two years ago, Seoul agreed to contribute $867 million toward US military costs in 2014, about 40 percent of the total. The deal called for the amount to rise annually at the rate of inflation.
Trump, the front-runner for the Republican nomination ahead of the November 2016 election, has made the complaint about Seoul for years. The political fact-checking website Politifact investigated similar statements he made on a television program in 2011 and rated his comments "false."
Asked if he would remove the 28,000 US troops from South Korea, Trump told CNN: "I would want South Korea to pay us a lot of money."
He noted he had just ordered 4,000 television sets from South Korea for his business.
"South Korea is a money machine. They pay us peanuts," Trump said. "I have many friends from South Korea. ... But South Korea should pay us and pay us very substantially for protecting them."
Trump told CNN that China should be responsible for solving the issue of North Korea's nuclear arms program, and if it does not, "we should be very tough on them with trade."
"You'd have China collapse in about two minutes," he said. "We have great power over China. We just don't know how to use it."