President Yoon Suk Yeol and first lady Kim Keon Hee on Sunday celebrated the return of 14th-century Buddhist relics that Seoul believes were illegally removed from the country about a century ago during the Japanese colonial era.

In his opening remarks, Yoon praised the relics as a "precious national heritage symbolizing the authenticity and spiritual lineage of Korean Buddhism," emphasizing that the improving ties between the allies were instrumental in achieving their return.

"It was a difficult issue that had long remained unresolved, but we were able to find clues to solve the problem as the relationship between South Korea and the United States grew closer," Yoon told participants.

Yoon further said, "The South Korean people and the government did not give up over the (stalled) talks, gathered strength and put in effort, eventually making people's wishes come true under Buddha's blessing."

The relics, returned Sunday to Hoeamsa, a Buddhist temple in Yangju, Gyeonggi Province, were a collection of the sariras of two monks in the 14th Century -- Master Jigong, an Indian monk also known as Dhyanabhadra; and his disciple, Master Naong Hyegeun -- as well as other fragments related to the Shakyamuni Buddha, Kassapa Buddha and Dipamkara Buddha.

Sariras are the bead-like remains found in the ashes of a monk's cremated body.

Some 10,000 people attended the ceremony at the temple of South Korea's Jogye Order, where Master Jigong's sarira was seen by the public for the first time in over six centuries.

Kim was quoted as saying by the presidential office that she was "honored to lend a helping hand, small as it would be, in making a wish that Korean Buddhist monks kept for a long time come true."

The event is Kim's first public appearance in 169 days since her visit to the memorial altar of the Ven. Jaseung, the former leader of South Korea's largest Buddhist sect, the Jogye Order, on Dec. 2.

The centuries-old relics have been housed in the Museum of Fine Arts, Boston, Massachusetts since 1939, when it acquired the relics from Japanese art dealer Yamanaka & Co. According to the presidential office, the symbolic remains were suspected to have been illicitly transferred from Korea to the United States during the period when Japan colonized the Korean Peninsula from 1910 to 1945.

The Jogye Order in 2009 requested the return of the Buddhist relics, including the sariras and their containers, as the relics' existence became known to South Korean monks in 2004.

The talks between the MFA Boston and the Jogye Order, however, fell through in 2013 as the MFA Boston refused to deaccession the containers and sought to separate the sariras from their containers, while the Jogye Order insisted that the sariras and containers could not be separated, according to the MFA Boston.

In April 2023, first lady Kim called for a resumption of a stalled negotiation over the relics' return, during her visit to MFA Boston on the sidelines of Yoon's state visit to the United States. Kim then said the resumption of talks "would hold significance if it takes place in the 70th anniversary of the South Korea-US alliance."

Following Kim's visit there, the Cultural Heritage Administration of South Korea and MFA Boston resumed the stalled talks for the first time in 10 years.

The Jogye Order, the CHA and the MFA Boston in February reached an agreement over the plans to permanently transfer the sarira in May, as Buddha's Birthday fell on Wednesday this year, and rent the containers for an undisclosed period of time. The relics were transferred from MFA Boston to South Korean monks in April.

Ven. Jinwoo, who leads Jogye Order, said during a ceremony that Kim "played a crucial role in (South Korean side's) negotiation with MFA Boston and MFA Boston's confirmation in transferring the relics."

Kim resumed official public duties Thursday, for the first time following her 153-day absence, after returning from Yoon's trip to the Netherlands in mid-December. She met her Cambodian counterpart, Pich Chanmony, as Yoon met with Cambodian Prime Minister Hun Manet in his office on Thursday.

Kim is currently facing an investigation by prosecutors into allegations she had violated antigraft law by accepting a luxury bag last year.