South Korea has agreed to a 13.9 percent increase in its contribution to the cost of hosting some 28,500 U.S. troops for 2021, the biggest annual rise in nearly two decades, its foreign ministry said on Wednesday.

Under the Special Measures Agreement (SMA), concluded after grueling negotiations of one and half years, Seoul will pay Washington 1.18 trillion won ($1.03 billion) for the U.S. Forces Korea (USFK). 

"The agreement served as an opportunity for the two countries to reaffirm the importance of the solid South Korea-U.S. alliance as the linchpin for peace and prosperity on the Korean Peninsula and in Northeast Asia, and the need for the stable stationing of the USFK," the ministry said in a press release.

The pact replaces an arrangement that expired at the end of 2019, under which South Korea paid about $920 million a year. Both sides agreed to freeze South Korea's contribution for 2020, the ministry added.

The six-year agreement "resolved a vacuum that had lasted about a year and three months," according to the ministry.

The ministry said it would take swift administrative steps and send the agreement to parliament for approval.

Washington and Seoul reached an agreement Monday on sharing the cost of maintaining U.S. military presence in South Korea with an increased contribution from the host country.

The official signing of the new SMA is likely to come during a visit to Seoul by U.S. Secretary of State Antony Blinken and Defense Secretary Lloyd Austin, which is expected to take place next week.

(With input from Reuters, Xinhua)

(Cover: South Korean and U.S. soldiers watching from an observation post during a joint live firing drill between the two countries in Pocheon, South Korea, April 26, 2017. /CFP)