The EMC - founded by former members of the Revolutionary Armed Forces of Colombia (FARC) rebels who reject the 2016 peace deal signed by that group - began talks with President Gustavo Petro's government last year, in a bid to end its part in Colombia's 60 years of war.
The announcement of the end of the ceasefire did not mention any effect on the overall negotiations.
The EMC and other rebel and armed groups often fight each other for control of illicit income streams like drug trafficking and illegal mining. Violence in many parts of Colombia has continued despite ongoing bilateral government ceasefires, such as that with the EMC.
The decree on Sunday called for "re-starting of military operations" in three provinces, Nariño, Cauca and Valle del Cauca, as of March 20.
(Reporting by Luis Jaime Acosta and Julia Symmes Cobb, Writing by Daina Beth Solomon; Editing by Aurora Ellis)
