Venezuela's crisis is spilling across the border into Colombia as Marxist rebels and right-wing paramilitaries recruit migrants to strengthen their ranks, according to five Colombian military commanders.

Violence still simmers in Colombia despite a 2016 peace deal with leftist FARC rebels, meant to end five decades of conflict. Dissident FARC fighters, the rebel National Liberation Army (ELN), right-wing paramilitaries and drug-trafficking gangs are battling each other and the military.

Keen for recruits, these armed groups are targeting Venezuelans as they traverse the porous 2,219-km frontier at illegal border crossings, according to the military officials, human rights officials and migrants themselves. Five military commanders told Reuters that as many as 30% of insurgents in Colombia's eastern border region are Venezuelans, willing to take up arms in return for food and pay.

Nationwide, an estimated 10% of fighters are Venezuelan, the commanders said. Their estimates were based on information from informants, deserters, captured rebels and residents. Reuters was not able to independently verify these figures. The head of Colombia's military and government spokesman on this issue, General Luis Fernando Navarro, told Reuters that armed groups were targeting Venezuelans because they were easier to recruit than Colombians. The military officers say they had interrogated some Venezuelans who had defected from armed groups and identified Venezuelan nationals killed in combat. They did not provide a total number for Venezuelan casualties. Several Venezuelan migrants told Reuters they had been approached by armed groups for recruitment on entering Colombia.