* Statement from FARC, ELN rebels likely to annoy President Santos
* ELN, government expressed interest in peace talks
By Helen Murphy
BOGOTA, July 1 (Reuters) - The top commanders of Colombia's two biggest rebel groups met in secret to discuss ways to bolster the nation's "guerrilla and revolutionary" movement, a sign the insurgent groups may be seeking to pressure the government for a joint peace effort.
In a statement published by both groups on Monday, the Revolutionary Armed Forces of Colombia, known as FARC, and the National Liberation Army, ELN, said they held a rare "summit" inside Colombia during which their leadership addressed the need for all rebel groups to be involved in peace talks.
Colombian government and FARC negotiators currently are holding talks in Havana in the hope of ending five decades of war. The two sides have clashed in recent days as they discuss how to incorporate the FARC, the Andean nation's biggest rebel movement, into the democratic process.
"We have held a summit in a fraternal environment of unity and camaraderie with the idea of strengthening advances toward a united guerrilla and revolutionary movement in our country," said the rebel groups' statement.
"Any solution to the internal conflict in our country through dialogue must inevitably advance through conversations with all Colombian insurgents," it said.
It was signed by FARC chief Timoleon Jimenez, known as Timochenko, and ELN leader Nicolas Rodriguez, known as Gabino.
In what appears to be the Marxist FARC flexing its political muscles as talks focus on what may be the most controversial item on a five-point agenda, the joint statement is sure to annoy President Juan Manuel Santos who has called on the rebels to stick to what was agreed upon before talks began in Cuba.
The FARC and the ELN, which have fought each other for control of drug trafficking routes but maintained a distance in recent years, discussed issues such as "deep changes to society, the economy, politics and Colombia's institutions," the statement said. It did not specify when the meeting took place.
A U.S.-backed offensive against both groups has severely weakened their numbers in the past decade, halving the FARC's fighting force to about 8,000 and whittling the ELN to less than 3,000. Still, neither are spent and are still able to hit hard at the nation's economic infrastructure, attacking oil and mining installations as well as military and civilian targets.
At the heart of their struggles against the government is what they see as unfair distribution of land and policies that excessively benefit the rich and foreign interests. More than 100,000 people have been killed in the conflict and millions displaced.
Santos has previously said he would consider negotiating peace separately with the ELN, the nation's second biggest rebel group, but only if it stops its attacks on military and civilian targets.
He has refused to consider any changes to Colombia's institutions or economic model as a condition for talks with either rebel group.
Efforts to rid Colombia of its reputation as one of the most dangerous places to do business have resulted in a rush of investment into areas that were once off-limits. Just a decade ago, armed rebels roamed almost unhindered over great swathes of land and prevented citizens from traveling in many areas for fear being kidnapped.
Both the ELN and the FARC have battled a dozen governments since they were founded in 1964 and are considered terrorist groups by the United States and the European Union.
The ELN was inspired by the Cuban revolution and established by radical Catholic priests. (Reporting by Helen Murphy; Editing by Bill Trott)
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