South Korea's chief negotiator in defense cost-sharing talks with the United States pledged best efforts Thursday to conclude negotiations on all major points this week, as he departed for Washington for a new round of talks.

Jeong Eun-bo and his US counterpart, Donna Welton, are set to meet in the US capital Friday for their first face-to-face talks on the sharing of the cost for stationing the 28,500 US Forces Korea since the administration of President Joe Biden took office in January.

"I think that, if possible, we intend to wrap up consultations on matters of principle through the upcoming talks," Jeong told reporters at Incheon International Airport, west of Seoul.

"When it comes to negotiations, it is difficult to make a prediction, and there could be more face-to-face talks if need be. But we will make our best efforts," he added.

While refusing to comment in detail, Jeong said that there are still some unresolved issues despite "considerable" progress in efforts toward the cost-sharing deal, called Special Measures Agreement (SMA).

"Negotiations are invariably proceeding toward a package deal, and they are still ongoing. So we cannot talk about the details of the negotiations and ask for your understanding," the negotiator said.

Asked about the possibility of the two sides finalizing a deal and announcing it in Washington this week, Jeong said, "We may not be able to do that given domestic procedures."

Hours before his departure, a US State Department official said that Seoul and Washington are "very close" to reaching agreement on an updated SMA.

The SMA talks appear to have picked up pace recently, as the Biden administration has pushed to strengthen America's alliances with democratic partners to shore up its global leadership and confront a string of challenges, such as China's assertiveness.

Since September 2019, the two sides have engaged in a grueling tug of war to reach the new SMA. But they failed to strike a deal amid the former Donald Trump administration's calls for a hefty increase in Seoul's payments.

Seoul has insisted that a 13 percent increase from the 2019 SMA is the "best offer" it could make. Washington had asked the ally to pay $1.3 billion a year, an increase of about 50 percent from the last deal.

The last one-year deal, which called for Seoul to pay about $870 million, already expired at the end of 2019. (Yonhap)