Speaking before the UN Labour Organization's annual assembly, Santos stressed that "peace is much more than just silencing the weapons."

"Building peace is like building a cathedral; it is a long and complex process that takes time. Brick by brick. And we are just getting started," he added.

Santos, who won the 2016 Nobel Peace Prize for his efforts to end a half-century of armed conflict with the former rebel movement FARC, said this would require "political, economic and social dimensions" that would take at least 15 years.

Santos and FARC leader Rodrigo Londono, better known as Timoleon "Timochenko" Jimenez, signed a deal in November 2016 to end the conflict.

But peace talks are still underway with the country's last active rebel force, the National Liberation Army (ELN), in Cuba.

Santos said he wanted to see "complete peace" in his country, where more than 260,000 people have been killed, nearly 83,000 remain missing and some 7.4 million have been forced to flee their homes over the past 50 years of conflict.

The fragile peace agreement could however be upended when Santos steps down in August.

Last Sunday, hardline conservative candidate Ivan Duque won the first round of Colombia's presidential elections and is favourite to defeat leftist Gustavo Petro in the June 17 run-off.

Duque has vowed to rewrite the FARC deal, which he believes is too lenient on the former guerrillas, and has expressed reservations about the negotiations with the ELN.