South Korea and the United States remain apart over how much Seoul will contribute financially to the presence of American troops on the peninsula, South Korea's top negotiator said Thursday.

"There are still big differences in the positions of the two sides," Hwang Joon-kook, special ambassador for the Special Measures Agreement (SMA), told reporters after two-day talks here with his U.S. counterpart, Eric John.

The allies are currently focusing not only on Seoul's appropriate share itself for the stationing of the 28,500-strong U.S. Forces Korea (USFK) but also on ways to improve the overall system for splitting the cost, according to Hwang.

The allies have shared the cost of USFK under the SMA since 1991. The previous agreement, signed in 2009, expires at the end of this year.

Setting the level of South Korea's contributions has always been controversial, especially in the nation.

Hwang said his government agrees to the need for overhauling the way it shares the cost for USFK.

He refused to provide details.

This week's round of negotiations was the fourth of its kind aimed at deciding the amount and method of Seoul's contributions over the coming years.

Multiple sources said South Korea has offered to keep the current yearly payment level -- some 870 billion won ($808 million), while the U.S. has requested an increase to 1 trillion won.

The U.S. is confronted with federal budget problems as well as growing North Korean threats. (Yonhap News)