South Korea and the United States could launch negotiations on sharing the cost for the upkeep of American troops here as early as the middle of next month, an official at Seoul's foreign ministry said Thursday.

The allies have been bracing for the negotiations on how much Seoul will pay next year for the stationing of the 28,500-strong US Forces Korea (USFK), as this year's Special Measures Agreement (SMA), a defense cost-sharing deal, is set to expire at the end of this year.

"I predict that (SMA) talks could open in mid-September at the earliest, after the Chuseok (autumn harvest) holiday," the official told reporters on condition of anonymity. Chuseok, one of the nation's biggest holidays, falls on Sept. 13 this year.

He expressed his expectation that Seoul and Washington may soon finalize the date for the launching of a new round of SMA negotiations.

Under this year's 10th SMA, Seoul agreed to pay 1.04 trillion won ($861.4 million), an increase of 8.2 percent from the previous year.

The next round of negotiations is expected to be tough as US Donald Trump has been increasing pressure on Seoul to jack up its financial contribution to the USFK, particularly ahead of his reelection battle.

Since 1991, Seoul has shouldered partial costs under the SMA -- for Korean civilians hired by the USFK, the construction of military facilities to maintain the allies' readiness and other forms of support. (Yonhap)