A State Department official on Thursday reiterated the United States' commitment to reaching a "mutually beneficial" defense cost-sharing agreement with South Korea, stressing the bilateral alliance is a "pivotal" relationship.

The official made the remarks a day after the two countries wrapped up their third round of negotiations over Seoul's share of the cost for stationing the 28,500-strong US Forces Korea under a deal, called the Special Measures Agreement. The current SMA is set to expire at the end of next year.

"The US-ROK alliance is a pivotal relationship so we will work together until we get a mutually beneficial agreement," the official said in response to a question from Yonhap News Agency. ROK stands for South Korea's official name, the Republic of Korea.

"The United States seeks a fair and equitable outcome to the Special Measures Agreement discussions for both countries that will strengthen and sustain the US-ROK alliance," the official added.

The official was responding to a question of whether the US has a timeline for the conclusion of negotiations and whether the two sides have made headway in the latest negotiations.

"We cannot discuss the specifics of ongoing consultations," the official said. "Consultations end when the two countries reach an agreement."

This week, Seoul's chief negotiator, Lee Tae-woo, and Linda Specht, US lead negotiator for security agreements at the State Department, led the three-day talks in Washington.

The two sides launched the negotiations in April, apparently earlier than usual, amid speculation that should former President Donald Trump return to the White House, he could call for a hefty increase in Seoul's share of the cost for the upkeep of USFK in a way that could cause tension in the alliance.

Since 1991, Seoul has partially shared the cost for Korean USFK workers; the construction of military installations, such as barracks, as well as training, educational, operational and communications facilities; and other logistical support. (Yonhap)