President Yoon Suk Yeol has thanked US President Joe Biden and first lady Jill Biden for their "truly warmest welcome" during his state visit to Washington last week, lauding relations between the two countries as "a blood alliance."

"Don't know how to thank @POTUS and @FLOTUS enough for their truly warmest welcome," Yoon tweeted Sunday, referring to the Bidens, adding that South Korea and the United States "are a blood alliance forged by the sacrifice of our young soldiers. An alliance of freedom and justice."

In a separate Twitter post Monday morning, Yoon said first lady Kim Keon Hee "also wishes to convey her many, many thanks" to the Bidens, especially the US first lady, "for preparing the most impressive state dinner."

"Hoping to return the favor with fine Korean cuisine in Seoul!" he said.

Yoon returned home Sunday from the six-day state visit designed to mark the 70th anniversary of the bilateral alliance this year. During the summit, Yoon and Biden adopted the "Washington Declaration," a joint statement committing the United States to a series of measures to better defend South Korea from North Korea's nuclear threats. (Yonhap)