WASHINGTON -- The US Department of Defense is working on details of how and when US vaccines will be provided to South Korean troops working with US Forces Korea, a Pentagon spokesman said Monday.

US President Joe Biden made a surprise announcement Friday that the US will help fully inoculate all 550,000 South Korean service members, who work closely with US troops in South Korea on a daily basis.

"Obviously we support the president's direction here to provide the vaccines to our ROK allies," Pentagon spokesman John Kirby said in a press briefing. ROK stands for the Republic of Korea, South Korea's official name.

"I think we're still working through the details of how that's going to occur," he added.

Kirby said the vaccines will "come out of US stockpiles."

The United States currently has three FDA-approved COVID-19 vaccines from Pfizer, Moderna and Johnson & Johnson.

Biden said the move will strengthen the US-South Korea alliance, but also safeguard US troops stationed in South Korea.

"There are 550,000 Korean soldiers, sailors, airmen who work in close contact with the American forces in Korea. We'll provide full vaccinations for all 550,000 of those Korean forces engaging with American forces on a regular basis, both for their sake, as well as the sake of the American forces," he said in a joint press conference with South Korean President Moon Jae-in after their first in-person summit in Washington.

Washington maintains some 28,500 US troops in South Korea.

South Korean defense ministry officials said that when and what types of vaccines will be provided have yet to be decided, but the ministry is making preparations to carry out the inoculation program smoothly.

"The South Korean and US governments are supposed to conduct consultations on the matter. Health authorities and the foreign ministries of the two nations will likely be involved, and we are drawing up a plan of our own to execute the plan right away," a ministry official said.

South Korea plans to inoculate troops in their 20s with Pfizer's vaccine, and those aged 30 and older have received AstraZeneca's.

Kirby also reiterated the importance of a close relationship between South Korean and US troops.

"Obviously, we've talked about this before, but training with our ROK allies is a significant component of our ability to meet our treaty commitments to South Korea," he said.

"And we constantly assess and review what training events might be best, and execute it in the most effective manner, and we're going to continue to do that going forward," he added.

He refused to provide any details when asked if the countries have plans to hold a large-scale joint field exercise.

The countries regularly hold joint military drills, but their exercises have largely been computer-simulated since last year due to the COVID-19 pandemic.

He also refused to comment on Seoul's role in case of a contingency in the Taiwan Strait, only saying that his country remains committed to assisting Taiwan in its self defense. (Yonhap)