Colombia's FARC rebels announced Wednesday they will observe a one-month unilateral ceasefire in response to an international appeal for an urgent de-escalation in the country's decades-old conflict.

The truce will start July 20, said Ivan Marquez, chief rebel negotiator at long-running peace talks in Havana.

He said the leftist rebels were acting on an appeal issued Tuesday by four countries supporting the peace talks, in order to dial back half a century of war after a recent spike in combat.

The goal of the truce, Marquez said, is to "create favorable conditions in order to advance with the opposing side toward a bilateral and definitive ceasefire."

There was no immediate comment from the Colombian government side on the rebel ceasefire announcement.