Seoul - Moon Jae-in, a liberal South Korean opposition leader who wants to improve ties with rival North Korea and pursue sweeping reforms, has become his party's presidential candidate, boosting his status as front-runner in next month's election of a successor to recently ousted President Park Geun-hye.If Moon is elected, it would end nearly a decade of conservative rule in South Korea, during which ties with North Korea have plunged to one of the lowest points in decades due to the North's nuclear and missile tests and the South's response. Jailed ParkAnalysts say Moon's softer approach toward North Korea could produce discord with Washington.Moon's popularity has surged since last fall, when a high-profile corruption scandal involving Park and a confidante flared. Millions took to the streets and called for Park's sacking, leading parliament to impeach her in December and the Constitutional Court to formally end her rule in March. Prosecutors arrested and jailed Park last week.Moon, who lost the 2012 election to Park, received a second chance to run for the presidency by winning the Democratic Party's nomination in party voting that ended on Monday. In a victory speech, Moon said if elected he would try to eradicate corruption; heal a deepening conservative-liberal divide and strengthen national security.Missile programmesMoon didn't touch upon North Korea. But he has previously called Park's hard-line North Korea policy a failure, saying it's time to use both sanctions and dialogue to persuade the North to resume negotiations on ending its nuclear and missile programmes.He has also been highly critical of Park's decision to let the United States place a high-tech missile defence system in South Korea that has angered both North Korea and China.