Al Jazeera has obtained exclusive footage of a Colombian contract killer detailing an alleged $25 million plot to kill Hugo Chavez, the Venezuelan president.

Geovanny Velasquez Zambrano says the money was offered by Manuel Rosales, one of Chavez's main political rivals, during a secret meeting in 1999.

A Colombian paramilitary group took up the offer, according to Zambrano.

Chavez has long said there is a plot by Colombia to kill him, and relations between the two countries are tense.

Francisco Dominguez, head of the Centre of Brazil and Latin American Studies at UK's Middlesex University, told Al Jazeera that so far, it has been impossible for Chavez's opponents to bring him down by political means.

"He's very popular. He's lost one of 16 elections only. So if anyone is desperate to get rid of him, the one neat mechanism to get rid of him would be assassination," Dominquez said.

"Chavez is pretty justified in thinking this guy's claims [Zambrano] were credible. It is credible that Rosales could have offered $25 million."