Delegates from the FARC and the government of former president Juan Manuel Santos sent a letter to UN chief Antonio Guterres in which they questioned the objectives of reforms announced by Duque to the Special Jurisdiction for Peace (JEP), which was set up to try former combatants accused of atrocities during the five-decade war.

"We express our deep concern at the attempts to seriously damage the implementation of the agreement, the structure and functioning of the JEP, as well as the system designed to honor the rights of the victims," they said.

Duque announced on Sunday that he will object before Congress to six of the 159 articles of the law that regulates the JEP, considered the backbone of the peace pact negotiated in Havana.

Duque won elections promising to modify the deal to prevent former FARC leaders from becoming lawmakers.

The pact guarantees the FARC 10 seats in Congress.