Colombian President Gustavo Petro on Monday suspended a truce with leftist guerrillas in four flashpoint regions  after authorities accused rebels of killing four Indigenous children.

Leftist Petro said the bilateral ceasefire "is suspended and all offensive operations are reactivated" in the regions of Meta, Caqueta, Guaviare and Putumayo.

Four children and teenagers from the Murui Indigenous community were executed in southern Colombia by dissidents of the now-disarmed Revolutionary Armed Forces of Colombia (FARC) rebels, authorities said Sunday.

The regions form a stronghold of FARC dissident guerrillas who refused to join a 2016 peace accord that saw most of the rebels lay down their arms and form a communist political party.

The rebel Estado Mayor Central responded to the news with a scathing attack on the government.

"The unilateral ceasefire will unleash war and the numbers of dead, injured and prisoners will multiply," the group said in a statement.

But the move was praised by the governor of Meta, Juan Guillermo Zuluaga.

"The patience was going to run out. The ceasefire suspension is not just for the vile murder of four children, but also for the kidnappings, extortion and other criminal behavior that never ends," Zuluaga wrote on Twitter.

The four Murui minors were executed on the border between the southern departments of Caqueta and Amazonas after defecting from a dissident faction of FARC called the Carolina Ramirez front, the country's human rights ombudsman said in a Sunday statement.

The front, which belongs to the Estado Mayor Central, was among the groups that adhered to a ceasefire proposed by the government several months ago and were set to begin new peace talks soon.

"Recruiting and killing children and adolescents from Indigenous communities are not exactly gestures of goodwill to achieve peace. In addition to being evident violations of international humanitarian law," the ombudsman noted.

Petro slammed the murders as "an atrocious crime, a blow to peace" and warned of "measures against these actions."

Complicating the situation on the ground, Colombian security forces and emergency personnel in an unrelated development are searching in the same region for four other Indigenous children who went missing ago after apparently surviving a small plane crash three weeks ago on the edge of the Amazon jungle.

- Government under fire for negotiating -

Late last year Petro announced a bilateral ceasefire with numerous armed groups.

But three of those truces have now ended following the breakdown of the peace process with the National Liberation Army guerrillas and the Gulf Clan drug traffickers.

"If the ceasefire is not effective in certain territories in protecting the lives and integrity of the population, then there is no sense in persisting with it," Petro wrote on Twitter.

Since coming to power last year, Petro has tried to negotiate peace with the country's various armed groups in a marked shift from his conservative predecessor's more bellicose approach to resolving the conflict.

This policy has triggered a hailstorm of criticism of Petro. The opposition has branded the armed forces too weak to prevent armed groups dictating the terms of peace.

"The main person responsible for the escalation in violence is Petro, who under the deceit of 'total peace' has left Colombia in the hands of terrorists," said right-wing opposition senator Maria Fernanda Cabal.

Colombia has suffered six decades of armed conflict between the state and various groups of left-wing guerrillas, right-wing paramilitaries and drug traffickers.

Petro, the first leftist president in Colombia's history, has opened talks with many of the armed groups, hoping to put an end to the violence in the world's largest cocaine producer.

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