The cease-fire began Dec. 15 and ended Jan. 15, Colombia Reports said.
During that period, FARC committed multiple acts of harassment in the town of El Doncello and is also responsible for two bombings that occurred in Anori and Briceno, the ombudsman's office alleged.
The Center of Resources for the Analysis of Conflicts said the cease-fire reduced violence by 65 percent.
FARC has been negotiating a peace agreement with the Colombian government since November 2012.
A new round of talks began Monday, Colombia Reports said.