Seoul, June 4 -- Lee Jae-myung, South Korea's new president, was briefed on Wednesday by the country's top military commander after formally beginning his single five-year term.

Lee received a security briefing over the phone from Joint Chiefs of Staff Chairman Kim Myung-soo, according to multiple media outlets.

The president called for the military to maintain a watertight readiness posture, praising soldiers for refraining from any active response to an "unlawful order" during the short-lived martial law imposition.

Lee was elected the country's 21st president in a snap election, caused by the ousted conservative President Yoon Suk-yeol's botched martial law bid last December.

He formally assumed his presidential duties, including the...