SEOUL (AFP) - South Korean software mogul Ahn Cheol Soo, whose independent candidacy enlivened last year's presidential election, plans to run for parliament in a by-election next month, his spokesman said on Monday.

Mr Ahn, 51, ran as an independent championing political and economic reform in the presidential poll but dropped out just weeks before the Dec 19 voting day to support the main opposition party candidate.

Hugely popular among younger voters, his decision to withdraw disappointed many seeking an alternative to the old liberal-conservative face-off between the established parties.

The man who ran his presidential campaign, independent lawmaker Song Ho Chang, said Mr Ahn, who has never held any political office, planned to return to South Korea next week after a two-month stay in the United States.

He will contend an April 24 by-election in Seoul, running on the same platform of "new politics" that he promoted in the presidential race, Mr Song said.

It was not immediately clear if he would run as an independent or under a particular party flag.

Mr Ahn withdrew from the presidential race to avoid splitting the liberal vote with the main opposition candidate Moon Jae In, who went on to lose the election to the conservative Park Geun Hye.

Negotiations between Mr Ahn and Mr Moon over who should step down were difficult and at times acrimonious, and Mr Ahn's later support for Mr Moon was seen as lacklustre.