Yoon, a conservative whose single five-year term begins in May, said during the campaign that he would make a stronger alliance with the United States the center of his foreign policy. He accused outgoing liberal President Moon Jae-in of tilting toward North Korea and China and away from the U.S. He also stressed a need to recognize the strategic importance of repairing ties with Japan despite a bitter dispute over wartime history.

Some experts say a Yoon government will likely be able to reinforce ties with Washington and improve relations with Tokyo, but will probably be unable to avoid friction with North Korea and China.

"I'll rebuild the South Korea-U.S. alliance. I'll (make) it a strategic comprehensive alliance while sharing key values like liberal democracy, a market economy and human rights," Yoon said in a televised news conference.

"I'll establish a strong military capacity to completely deter any provocation," Yoon said. "I'll firmly deal with illicit, unreasonable behavior by North Korea in a principled manner, though I'll always leave open the door for South-North talks."

After his election win, he spoke with U.S. President Joe Biden on the phone. According to a White House statement, Biden congratulated Yoon and emphasized the U.S. commitment to the defense of South Korea. It said the two also agreed to maintain close coordination in addressing threats posed by North Korea's nuclear and missile programs.

North Korea didn't immediately comment on Yoon's victory. In recent weeks, it has tested a spate of sophisticated, nuclear-capable ballistic missiles in what experts call an attempt to modernize its weapons arsenal and pressure the Biden administration into making concessions such as an easing of sanctions amid stalled nuclear diplomacy.