BOGOTA (Reuters) - Colombia must allow FARC rebel dissidents to demobilize and join reintegration efforts if it wants to tackle armed groups operating along its border with Venezuela, rights group Human Rights Watch (HRW) said Wednesday.

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The Revolutionary Armed Forces of Colombia (FARC) rebels largely demobilized under a 2016 peace deal, becoming a legal political party, but several top commanders last year rejected the peace deal and re-armed.

There are an estimated 2,500 FARC dissident fighters, according to intelligence sources.

“We think that the state should find means of weakening these groups not based just on the use of force but also in implementing policies that permit dissidents to demobilize and draw them into the peace process,” said Jose Miguel Vivanco, director of HRW’s Americas division.

Dissidents, the National Liberation Army (ELN) rebels and Venezuelan armed group the Patriotic Forces of National Liberation (FPLN) are responsible for numerous abuses in the eastern Colombian province of Arauca and neighboring Venezuelan state Apure, where they operate with almost total impunity, HRW said in an earlier statement.

Children recruited from both sides of the border can be as young as 12, the report said. While child recruitment by the FPLN appears to be uncommon, HRW said the ELN and FARC dissidents offered payment to encourage children to join up.

Because the FARC dissidents are considered criminals by Colombian authorities, children recruited by the group have no legal avenues to demobilize if they escape as adults, unlike their counterparts recruited by the ELN, the rights group said.

HRW also called on the United States, Canada, the European Union and governments across Latin America to impose targeted sanctions - including traffic bans and asset freezes - on senior Venezuelan officials complicit in abuses by armed groups.

On Monday, U.S. Secretary of State Mike Pompeo called Venezuela a failed state and pledged further action during a visit to Bogota.

Colombia last week opened an investigation into a former general over accusations he spied on judicial officials, journalists and other military members.

Vivanco said HRW would work to determine whether the equipment used in the alleged spying was donated by the United States as part of long-standing binational efforts to fight organized crime.

“If (the equipment) is North American, if it has been donated by the United States, there should be serious consequences,” Vivanco said.