The leader of a group of peasants who are demanding land in northern Colombia was gunned down by unidentified individuals, President Juan Manuel Santos said.

"We strongly condemn the murder of Jairo Martinez, who was demanding land," Santos said in a Twitter posting.

"A quick investigation has been ordered to severely punish" those behind the killing, the president said.

Martinez was murdered Friday in a rural area outside Monteria, the capital of the northern province of Sucre, where Revolutionary Armed Forces of Colombia, or FARC, and National Liberation Army, or ELN, guerrillas, as well as drug traffickers, operate.

Martinez was the leader of a group of peasants who are demanding the return of lands stolen from them by illegal armed groups in the Montes de Maria region.

The Santos administration is implementing a land restitution program covering more than 3.5 million hectares (8.64 million acres) through the end of its term in 2014.

More than 50 peasant leaders evicted from their lands have been murdered in Colombia since 2002, non-governmental organizations, such as the National Movement of Victims of State Crimes, or Movice, say. EFE