FARC guerrillas returned Thursday to their hideouts in the Colombian jungle and mountains after voters rejected a landmark peace deal with the government, Red Cross sources said.

The Marxist rebels had gathered in a remote area known as El Diamante in southern Colombia in preparation for a UN-monitored disarmament process.

But they returned to their positions after Sunday's shock referendum result, said sources at the humanitarian group, which helped facilitate their transport.

"They traveled unarmed and in civilian clothing," said a source from the International Committee of the Red Cross.

The sources would not say how many of the FARC's nearly 6,000 fighters were involved, or what kind of transport they used.

The redeployment comes as Colombia teeters between war and peace.

President Juan Manuel Santos and the FARC have been left scrambling to save their peace accord -- the product of nearly four years of negotiations -- after right-wing hardliners led a successful campaign to vote against it.

The leader of the "No" camp, former president Alvaro Uribe, argued the deal offered the rebels impunity for their crimes and would put Colombia on the path of "Castro-Chavismo" -- a reference to the far-left governments of Cuba and Venezuela.

Santos, who has staked his legacy on making peace, has warned that the country is now in a "very dangerous limbo."

He said the army would halt its ceasefire with the FARC at the end of the month if no solution is found -- though he later said the deadline could be extended.

The opposition wants Santos to renegotiate a tougher deal with the rebels.

FARC leaders have vowed they are committed to making peace, but it is unclear whether they will be able to sell a new deal to the rank and file.

In the meantime, they have ordered their fighters back to "secure sites."

FARC commander Pastor Alape said on Twitter that the order aimed to avoid "provocations" from opponents of the peace deal.

The Colombia conflict has killed more than 260,000 people and left 45,000 missing over five decades, drawing in several leftist guerrilla groups, right-wing paramilitaries and drug gangs.

The Revolutionary Armed Forces of Colombia (FARC), the oldest and largest rebel group, was to relaunch as a political party under the deal.