(DailyMail) -- Moon, speaking during his formal oath of office, didn't elaborate. But he favors a softer approach to dealing with North Korea and its nuclear and missile ambitions than his conservative predecessors.

Moon also said that he will negotiate with the United States, the South's top ally, and China, Seoul's top trading partner, over a contentious U.S. missile-defense system deployed in the South. Beijing says the system allows Washington to spy on China's military operations.

South Korean President Moon Jae-in has taken the oath of office in a ceremony at the National Assembly in the capital, Seoul. The oath took place hours after his presidential term began.

Moon assumed presidential duties earlier on Wednesday after the National Election Commission declared him winner of a presidential by-election to replace ousted leader Park Geun-hye, who now awaits a corruption trial in jail.