Gustavo Petro takes on the job of mayor of Bogota from his now imprisoned predecessor Samuel Moreno [Reuters]

A former leftist fighter has been sworn in as the new mayor of Bogota, the second most important political position in Colombia after the president.

In his first speech on Sunday, Gustavo Petro, 51, focused on security and new measures to protect children.

He has implemented a ban on the carrying of guns by civilians, with the exception of the police and the army.

In 2011, police records showed at least 1,500 violent deaths in Bogota.

Petro is an economist who in the past has won seats in the House of Representatives and the Senate, but who started his political career in the 1980s as part of the M-19, or 19th of April Movement.

The leftist armed group was created in response to an electoral fraud in April 1970, and by 1985 had become the second largest such group after the FARC.

Petro started peace talks with the Colombian State in 1990 and the M-19 became a political party.

As a congressman and senator, he denounced the links between paramilitaries and the political elite in Colombia.

His constant accusations forced the Supreme Court to open an investigation which ended in the jailing of more than 60 politicians.

Petro arrives in office at a critical moment. His predecessor Samuel Moreno, who is now in prison, left a $1.2bn vacuum in the city's budget and is also accused of extorting money from businessmen.