Bogota, Colombia - The commander of Colombia's largest guerrilla group on Thursday backed calls for warring militias to unite to repel any US military operations in the country.

"If it's to defend the homeland against foreign aggression, we'll join the fight," ELN leader Antonio Garcia told AFP, responding to calls for factions to unite.

President Donald Trump, after removing Nicolas Maduro as president of Venezuela in a violent coup, has suggested US forces may train its guns on Colombia next.

He has used the familiar pretext of Bogota not doing enough to stop drug trafficking to the US.

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Ostensibly a leftist insurgent force, the 6,000-person-strong ELN doubles as one of Latin America's most powerful drug-trafficking organizations,

It controls a swath of the Colombia-Venezuela border region and has close ties to Caracas. ELN fighters staged military exercises in December as Trump's threats against Venezuela escalated.

Colombian intelligence sources allege that Garcia himself lived in Venezuela until recently.

Other Colombian guerrilla groups have reacted angrily to Maduro's removal from power, describing it as a US colonialist plot.

Ivan Mordisco, Colombia's most wanted rebel, who leads his own dissident group, has called for a unity pact to repel the US imperialism.

"We know we have had our differences in the past... but today we are facing a common enemy," said Mordisco, leader of the remnants of the dissolved FARC armed movement, also thought to have rear bases in Venezuela.

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"We summon you urgently to a summit of insurgent commanders from Colombia and all over our America," he said, in a video sent to media.

"Let us forge a great insurgent front to drive back our enemies."

In a message from hiding, Garcia told AFP that his group would be willing to fight US forces.

The ELN "does what it must at each stage of the struggle," he said.

Colombia's Defense Minister Pedro Sanchez has said guerrillas seek unity because "the threat of lethal action" against them is now greater.

Under intense pressure from the US and after a series of clashes with Trump, Colombia's president Gustavo Petro has agreed to "joint action" against the ELN and other drug smugglers.

Trump recently told Petro to "watch his a***" and hit the Colombian president and his family with sanctions. The former guerrilla fighter responded by saying he was prepared to personally take up arms in defense of his country.

But after an ice-breaking phone call, Trump will host him at the White House in February.