Leftist candidates won a host of new seats in Colombia's local and regional elections, results showed Monday, including a former guerrilla fighter in the Bogota's mayor's office.

They were the first elections since the 2010 victory of center-right President Juan Manuel Santos who took the reins from the hard-right Alvaro Uribe, whose politics appeared rebuked by the electorate after he personally campaigned for a number of losing candidates.

Colombians elected governors in 32 departments and more than 1,000 mayors, as well as representatives to their state assemblies and municipal councils.

The regional elections are considered to hold the greatest personal risk for candidates, who come under pressure from guerrillas or paramilitary groups vying for control over local governments.

Notably in what was thought to be Uribe's safe territories -- like the northwestern department of Antiquia where he was governor before his 2002-2010 -- the candidates he backed for governor lost, as well as his pick for Medellin mayor.

In the capital Bogota, Gustavo Petro, who once belonged to the nationalist leftist rebel movement M-19, swept to victory.

The win was important, political analyst Fernando Girado told AFP, as it "marks not only the first time a former guerrilla had been elected to a position of such power in Colombia, but because as senator he directly confronted Uribe."

The legacy of Uribe's rightist government, said observers, was seriously tainted by a number of corruption scandals, among them charges of eavesdropping on opponents and illegal surveillance of judges, politicians and journalists.

The elections marked the end of a campaign season marked by strong violence, with some 41 candidates murdered this year leading up to the vote, according to an observer group's tally.

An upsurge in leftist guerrilla attacks in October attacks had left 23 soldiers dead, as guerrillas of the Revolutionary Armed Forces of Colombia (FARC) mounting attacks on security forces.

The FARC is the oldest and largest guerrilla group in Colombia. It has been active for 47 years and has an estimated 8,000 fighters under arms, according to defense ministry figures.