Jeremy McDermott BBC correspondent in Colombia

Up to 60 people have been killed in Colombia in a battle for territory between Marxist guerrillas and right-wing paramilitaries.

The territory in question contains drug crops and gold mines - both key money-earners for the warring factions.

President Uribe has promised a crackdown

The new President, Alvaro Uribe, will be concerned at the fresh outbreak of violence, but comforted by the fact that it was two of the country's illegal armies killing each other, in an area where the state has little, or no, presence.

Mr Uribe took power on Wednesday amid the firing of guerrilla mortars in the capital, Bogota.

An increasing feature of the 38-year civil conflict has been direct and large-scale clashes between the illegal armies of the right and left for control of territory and strategic resources.

As in this latest battle in the northern province of Bolivar, the Marxist guerrillas have come off best.

Colombia has been at war for nearly four decades

General Martin Orlando Carreno, the divisional commander in the area of the fighting, said that some 30 paramilitaries had been killed compared with 20 guerrillas from the country's two main rebel groups, the Revolutionary Armed Forces of Colombia (FARC) and the National Liberation Army (ELN).

The two guerrilla groups joined forces in this part of the country to face a paramilitary invasion that began about three years ago.

Drugs and extortion from businesses form the main sources of revenue for the illegal armies, along with the guerrillas' speciality of kidnapping, which all told is said to fund the warring factions to the tune of almost $1bn a year.

President Uribe has to find a way to increase the desperately stretched defence budget to compete with the ever-growing warring factions and to find a way to recover the half of the country they control.