BOGOTA, Colombia — The head of Colombia’s last remaining rebel group has ordered guerrillas to stand down ahead of a bilateral cease-fire taking effect this weekend that is an important milestone in efforts to end a half century of political violence in the South American nation.

In a rare video posted online Friday, Nicolas Rodriguez said he was confident rebels belonging to the National Liberation Army would obey orders not to attack government troops or take other offensive actions banned by the cease-fire — a tacit acknowledgement of the difficulties ELN commanders have had controlling their estimated 1,500 troops.

“I have no doubt of your loyalty and that you will fulfill this commitment to the last consequences,” said Rodriguez, sitting before a laptop computer and speaking into a guerrilla field radio with several armed and masked rebels standing nearby.

Hopes were high for peace talks between the government and ELN that started in February in Ecuador following an agreement last year that led to the disarmament of the much larger Revolutionary Armed Forces of Colombia.

But progress has been slow as the ELN has remained on the offensive and stepped up attacks on oil pipelines. Just this week, the group was blamed for two simultaneous attacks on a major oil pipeline near the border with Venezuela that dumped crude in several rivers and farms affecting 700 families.

President Juan Manuel Santos on Friday signed a decree ordering troops not to attack ELN rebels once the temporary cease-fire takes effect at midnight Saturday. Santos pointed out that this would be the first bilateral cease-fire the ELN has signed in the history of its Cuban-inspired insurgency.

The cease-fire will initially last until Jan. 9, after which it can be renewed by mutual consent. As part of the agreement, the ELN has pledged to renounce hostage-taking, recruitment of of minors and attacks on infrastructure. The government in turn must improve conditions for jailed rebels as well as boost protections for leftist activists in areas dominated by the ELN.

“As Pope Francis has urged, we must never stop pursuing peace,” Santos said.

According to the protocol signed by government and rebel negotiators, observers from the United Nations will fan out across the country to 33 areas where the ELN is strongest to monitor the cease-fire’s implementation. They will be assisted by the Roman Catholic church, from which many of the ELN’s founders — priests and seminary students — hail.