SEOUL - South Korea's leading presidential hopefuls were crisscrossing the country on the final day of campaigning on Monday before converging on Seoul, vowing to revive an ailing economy and put months of turmoil over a failed martial law attempt behind them.

Tuesday's election was triggered by the ouster of Yoon Suk-yeol who briefly imposed martial law in December, stunning South Koreans who had come to believe the days of using the military to intervene in the democratic process were long past.

Liberal frontrunner Lee Jae-myung vowed to mend the social division that deepened in the aftermath of Yoon's martial law, but said his opponent and Yoon's People Power Party must be held accountable, branding them "insurrection sympathizers".

"We are at a historic inflection point of whether we go on as a democratic republic or become a country of dictators," Lee told a campaign rally in the battleground capital.

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Later he said the top priority as president if elected would be to take urgent steps to address the economy, adding he would first turn his attention to the cost of living for middle- and low-income families and the struggles of small business owners.

After sweeping through key swing vote regions and the stronghold of his main conservative opponent, Kim Moon-soo, Lee focused on the capital region home to the highest concentration of the country's 44.39 million voters.

Kim started the final day on the southern island of Jeju before crossing the country north, calling Lee a "dangerous man" who would abuse the office of president and the parliament controlled by his Democratic Party in an unchecked manner.

The conservative candidate once again apologized on Monday for Yoon's martial law and pledged to undertake political reform.

The two leading candidates were scheduled to wrap up three weeks of official campaigning at midnight in Seoul, with polls set to open at 6 am (2100 GMT on Monday) on Tuesday across the country.

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The winner, who will be certified on Wednesday, will have just a short few hours before taking office without the usual two-month transition as Yoon was removed by the Constitutional Court on April 4 for grave violation of his lawful duties.