ELN guerrillas on Monday branded as "unacceptable" conditions set by Colombian President Ivan Duque to restart peace talks in Cuba aimed at ending their insurgency.
Right-winger Duque gave the Marxist rebels a one-month deadline after his inauguration on August 7 to convince him they are serious about laying down arms and re-entering civilian life.
That cut-off point expired on Friday.
By refusing to recognize agreements reached under Duque's predecessor, Juan Manuel Santos, "and unilaterally placing unacceptable conditions, this government is... ending the process of dialogue" aimed at reaching a peace agreement, National Liberation Army (ELN) negotiators in Havana said in a statement.
The statement called for restarting talks "with no further delays."
Colombia's high commissioner for peace, Miguel Ceballos, said the "Colombian government is continuing to express its desire for peace."
But, speaking to Colombian Caracol Radio, he said it was doing so "with concrete actions and not rhetoric."
The main sticking point for Duque's government is ELN hostages.
It says the release of those detainees -- believed to be 16 -- is a precondition for any resumption of peace talks.
With an estimated 1,500 fighters, the ELN is the last recognized armed rebel group operating in Colombia. Authorities believe it is financed through drug trafficking and illegal mining.
It has said it is prepared to release its hostages and last week let go three soldiers captured a month earlier.
But Ceballos doubts the ELN's sincerity, saying they have carried out 30 "armed actions" in the last month alone.
"I would not interpret that in any other way than the ELN continuing to ignore the government's will," he said.
Santos won the Nobel Peace Prize for signing the historic accord with the much larger FARC rebels in 2016, turning that armed group into a political party after more than 50 years of insurrection.