The U.S. forces stationed here had an unused, Seoul-contributed defense fund of more than 600 billion won ($567 million) as of January, though the amounted declined from five months earlier, government data showed Thursday.

The unspent defense cost for United States Forces Korea  came to 621 billion won as of the end of January, down some 90 billion won from the end of August in 2013, according to the data by the foreign ministry.

The amount of unspent fund at end-January accounted for about 77 percent of what the South Korean government has earmarked for this year's annual defense sharing funds intended for USFK.

Since first signing a Special Measure Agreement in 1991, South Korea has annually contributed funds to co-share the financial burden of USFK defense activities.

The figure is seen as backing up opposition lawmakers' criticism that Seoul and Washington's newly renewed SMA sharply increased South Korea's annual financial contributions even though USKF is sitting on a large amount of unspent fund.

In response to such criticism, the foreign ministry said, "Most (of the unspent fund) is expected to be used up within a few years, given a flurry of construction projects (being led) ahead of USFK's military base relocation in 2016."

Seoul is also required to pay an additional 303 billion won to USFK as the country did not fully pay its contributions for the 2011-13 period, the ministry also said.

The data came as the new SMA deal has been pending in the National Assembly since early February due to opposition lawmakers' resistance.

The Seoul-Washington defense treaty had initially put the burden of financing U.S. defense activities solely on the U.S. side. The allies signed their first SMA in 1991, and the deal has since been renewed intermittently.

The USFK forces are stationed in South Korea mainly as a deterrent against North Korean threat, a legacy of the 1950-53 Korean War. (Yonhap)