The U.S. president promised to defend South Korea in meetings that featured a rendition of “American Pie” by his Korean counterpart.

U.S. President Joe Biden has warned of dire consequences for North Korea’s regime if it launches a nuclear attack, as he seeks to reassure South Korea of Washington’s commitment to defending its ally against the threat from the North.

“A nuclear attack by North Korea against the United States or its allies or partners is unacceptable and will result in the end of whatever regime, were it to take such an action,” Biden said on Wednesday at a joint news conference after meeting his South Korean counterpart, President Yoon Suk-yeol, in the White House.