Seoul, June 4 -- Lee Jae-myung was sworn in as South Korea's new president on Wednesday after formally beginning his single five-year term earlier in the day.

The country's 21st president took the oath of office in the National Assembly building, saying in a televised inaugural address that he will serve all people whomever they supported in the presidential election.

Lee of the majority liberal Democratic Party won 49.42 percent of support, defeating his archrival Kim Moon-soo of the conservative People Power Party by a wide margin of 8.27 percentage points.

The president assumed duties without a transition period as he won the snap election, triggered by the removal of his predecessor from office over a botched martial law bid last Dec...