Colombia's two leftist rebel groups have agreed to form a military alliance to step up attacks against the government of US-backed President Alvaro Uribe.
The accord, which could herald an escalation in Colombia's four-decade-old guerrilla war, was struck after secret meetings between top commanders of the Revolutionary Armed Forces of Colombia, known as FARC, and the smaller National Liberation Army, or ELN.
"The leaders of the FARC and the ELN have agreed to join military forces against the government of Uribe. We will now carry out nationwide joint military operations," a rebel involved in the negotiations said in the mountains of eastern Colombia.
The accord came as Mr Uribe conducts peace talks with right-wing paramilitary outlaws who have targeted rebels in a war that kills thousands every year.
Rebels said the FARC and the ELN, who have been fighting the government since the 1960s to install a socialist regime, will keep "separate political and structural organisations."
In practice, the Soviet-inspired, 17,000-strong FARC is likely to dominate an alliance with the pro-Cuban ELN, which has about one-third as many fighters.
The FARC, Latin America's oldest guerrilla force, has in the past tried to absorb the ELN. The FARC and the ELN formed an umbrella group in the 1980s but it quickly fell apart, leaving rebels to form regional tactical alliances.
The FARC is economically and militarily stronger than the ELN thanks to its participation in the drug trade, analysts say.
The ELN has been seriously weakened in recent years by military defeats at the hands of the army and right-wing outlaws.