Desperate Venezuelan migrants are being recruited by militants in Colombia in exchange for food, Colombian military commanders have said.

Millions of Venezuelans have fled the country's spiralling political and economic crisis, and armed groups in Colombia are targeting them as they cross the 1,400-mile border.

Migrants say they have been approached at the border, offered food, accommodation and paramilitary training, and encouraged to pick coca, the raw material for cocaine.

Military leaders have said that as many as 30 per cent of insurgents in Colombia's eastern border region are Venezuelans, willing to take up arms in return for food and pay.

People walk along a pathway near the Colombia-Venezuela border on the outskirts of Cucuta, Colombia, earlier this month - a border region where militants have been looking to recruit

Violence still simmers in Colombia despite a 2016 peace deal with leftist FARC rebels, which was meant to end five decades of conflict.

Dissident FARC fighters, the rebel National Liberation Army (ELN), right-wing paramilitaries and drug-trafficking gangs are still battling each other and the military.

'Recruitment of Venezuelans is happening,' said Colonel Arnulfo Traslavina, military commander of a special unit battling armed groups in Colombia's eastern border state of Arauca.

'The ranks of illegal armed groups are increasing. It's a major threat to Colombia.'

An estimated 1.3 million Venezuelan migrants have settled in Colombia in recent years, fleeing shortages of food, electricity and water.

Several Venezuelan migrants said they had been approached by armed groups for recruitment on entering Colombia.

'They said I'd get clothes, food, money, accommodation, a cell phone,' said Gregorio, a 20-year-old Venezuelan migrant who said he was asked to join an unspecified group in the mountains as soon as he waded across the Tachira River onto Colombian soil.

'I was tempted, but scared... I'd been told there were bad people offering such things and I didn't want to join,' said Gregorio.

In addition, Army Colonel Rodolfo Morales said migrants were also being drafted by drug trafficking groups to pick coca, the raw material for cocaine.

Venezuelan migrants (pictured here queuing at a border post) are being recruited by militants in Colombia in exchange for food, Colombian military commanders have said

Antonio, another Venezuelan migrant who declined to give his second name, said that after crossing the border he was offered money by unidentified men to go into the jungles around Tibu - a border town around 115 km north of Cucuta in the dangerous Catatumbo region - to pick coca leaves.

'I'd rather go hungry than go with them,' said the 33-year old from the central Venezuelan state of Carabobo.

Eddinson, 26, a migrant from Venezuela's coastal state of Aragua, said he and three other Venezuelans were approached by armed men who identified themselves as paramilitaries as they trekked through the mountains of Santander province near the border.

Eddinson said the leader of the eight armed men - who were dressed in khaki uniforms - tried to recruit them.

'He said that training would last six months. We'd be given salaries according to rank,' said Eddinson, adding that he and the other Venezuelans declined the offer.

'He told us that we'd know our start date but not when we could leave.'

Most Venezuelans do not come to Colombia to enlist in insurgent groups but with almost nothing in their pockets, the prospect of food and shelter is enticing, said Deisson Marino, human rights ombudsman for the border region of Arauca.

'They end up enrolled in a war that has nothing to do with them,' said Marino, whose job involves traveling to remote areas and speaking to victims of the conflict and armed groups.

People are seen next to the Tachira river near the Colombian-Venezuelan border last month

Nationwide, an estimated 10 per cent of fighters are Venezuelan, the commanders said.

Their estimates were based on information from informants, deserters, captured rebels and residents.

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.

Rebel numbers are small compared with the 250,000 combat troops in the armed forces but Colombia's rugged jungle terrain - spread across a country the size of France and Spain - makes it difficult for the military to tackle small, mobile units of fighters.

Military officers say they had interrogated some Venezuelans who had defected from armed groups.

A FARC dissident, who asked not to be identified, said the group was also present on Venezuelan soil and was recruiting Venezuelans.

Venezuela's government has acknowledged that the ELN and dissident FARC are present on its territory.

It has said it does not support the groups or tolerate their presence, and that its troops pursue them as they would any other illegal group.

FARC, which became a political party after the peace deal and kept its former acronym, has publicly expelled the armed dissidents.