By Patricia Zengerle and David Brunnstrom
WASHINGTON (Reuters) -South Korean President Yoon Suk Yeol told U.S. lawmakers on Thursday it is necessary to speed up trilateral cooperation with Japan and the United States to counter increasing North Korean nuclear threats, and said the world must not "shy away" from promoting freedom for the North.
Yoon, on the fourth day of a state visit to mark the 70th anniversary of the U.S.-South Korean alliance, also vowed in a speech to a joint meeting of Congress that South Korea would actively work to safeguard the freedom of the people of Ukraine and support their reconstruction efforts.
He was greeted with a standing ovation and repeated loud cheers in a packed House of Representatives chamber by members of the House and Senate.
Yoon paid tribute to the U.S. sacrifice to defend freedom against communism in the 1950-53 Korean War, as well as the work of 19th century U.S. missionaries to advance women's status in Korea.
"Korea will never forget the great American heroes who fought with us to defend freedom," he said.
On Wednesday, Yoon met President Joe Biden at the White House and the United States pledged to give South Korea more insight into its nuclear planning over any conflict with North Korea, amid anxiety over Pyongyang's growing arsenal of missiles and bombs.
Yoon told Congress the alliance must stand united to deter North Korea's "reckless behavior" and highlighted his efforts towards rapprochement with neighboring Japan after years of strained relations, by saying:
"Along with close Korea-U.S. coordination, we need to speed up Korea-U.S.-Japan trilateral security cooperation to counter increasing North Korean nuclear threats."
Yoon became the seventh South Korea leader to address Congress, underscoring the close relationship between Seoul and Washington.
Such addresses to Congress are generally reserved for the closest U.S. allies or major world figures. The last such address was by Ukrainian President Volodymyr Zelenskiy in December.
Yoon condemned Russia's war against Ukraine as a violation of international law and vowed to help Ukraine, just as democracies had helped Seoul in the Korean War.
"We will actively work to safeguard the freedom of the people of Ukraine and support their efforts in reconstruction," he said.
(Reporting by Patricia Zengerle, David Brunnstrom and Susan Heavey; Editing by Alexandra Hudson)