The BBC's John Simpson examines Colombia's pro-Communist revolutionary forces

For four decades they have fought a guerrilla war; more than 35,000 people have died in the last 10 years alone.

Their main demands are for sweeping land ownership reforms, an end to free market economic policies, greater social spending and limits on the role of foreign multinationals in Colombia's oil industry.

The Revolutionary Armed Forces of Colombia (FARC) is estimated to have about 5,700 active armed members.

A Marxist group, it is said to finance its operation through kidnappings and links with Colombia's infamous drug cartels.

In 1997, 1,822 cases of abduction were reported in Colombia, 900 attributed to FARC.

Other groups

It has formed a loose alliance, the Coordinadora Nacional Guerrillera Simon Bolivar (CNGSB) with two other groups, the ELN and EPL.

The ELN, the National Liberation Army, was formed in 1965 and is a pro-Cuban, Marxist movement. It is estimated to have about 2,500 active armed members.

An estimated 500 members of the EPL, the People's Liberation Army, are continuing an armed struggle. Most of the organisation's members abandoned violence as a tactic in 1991 when the Maoist movement became a political party.

Strategic target

One of FARC's main targets has been the control of a key road leading into the capital, Bogota, from the mountains in the north-west.

The road is the main route for food and petrol supplies to the city and has been regularly cut by the guerrillas.

The road to Bogota is often cut by guerrilla attacks

And they have scored notable successes against the army, which is made up largely of conscripts.

In August 1996 FARC guerrillas attacked a military base in the south east killing 26 soldiers and capturing 60 others.

They were released 10 months later after the army had pulled out of a large area of territory.

During the March 1998 congressional elections 83 soldiers were reported killed during a battle with FARC.

Drugs link

Evidence of the link between guerrilla movements and drug cartels increased during 1996, when, in March, FARC attacked a drugs control police unit.

FARC and ELN also launched a major offensive at the same time that coca growers were holding protests about a crop-spraying eradication programme.

Despite their victories BBC correspondent John Simpson says some guerrillas feel they have reached a stalemate.

And Rocio Lopez, a local official who is in contact with the guerrillas, says she is sure both they and the government finally want to negotiate.