A flamboyant US-backed lawyer who has never held public office narrowly won Colombia’s presidential run-off on Sunday, swinging the country hard to the right on a promise to wage war against drug-running guerrilla groups.

With more than 99 per cent of polling centres reporting, Abelardo de la Espriella had 49.65 per cent of the vote, an unassailable lead over his rival, left-wing Senator Ivan Cepeda who trailed at 48.70 per cent, according to official results.

Cepeda said on Sunday he will await a final, ballot-by-ballot ‌check of an initial vote count, saying his campaign is challenging results from some 33,000 ballot boxes.

The difference ‌between the two men is equivalent to ‌some 246,000 ‌votes. The head of ‌the national registrar Hernan Penagos ⁠said separately that verification was beginning ⁠at a municipal level and would soon extend across the ‌country. ‌A final count, overseen by notaries and judges, is required by Colombian law.

In Bogota, De la Espriella supporters wearing the canary yellow national football jersey he adopted as a campaign uniform waved flags and blew horns as victory became clear.

The hyper-fractious election campaign was marred by guerrilla bomb attacks, hundreds of threats against candidates and the murder of a leading conservative presidential hopeful.