We should be prepared for the possibility that we will suffer bigger terrorist strikes

President Pastrana

The Defence Minister, Gustavo Bell, said the armed forces would control public safety in the regions, which have come under rebel attack since the collapse of peace talks last week.

Many small towns and several large cities have been left without power after rebels began blowing up electricity pylons.

In other areas, the rebels have destroyed bridges and cut off telephone lines.

The army says it has hit back with a number of aerial raids against rebel targets.

The newly declared war zone includes spots just 75 kilometres (50 miles) from the capital Bogota, as well as an area the size of Switzerland, which for three years was a FARC safe haven.

Click here for a map of the former FARC safe haven

Following the declaration, military commanders in the war zone will have special powers to restrict people's movements and examine identity papers, as well as prohibit the bearing of arms and alcohol consumption.

Pastrana has called for unity

"If we are going to be successful, it's going to be necessary for the people to help by assisting the security forces," Interior Minister Armando Estrada said.

Last week, after the kidnapping of a senator, Colombian President Andres Pastrana sent the army in to reclaim the area which had been ceded to the rebels.

On Thursday, in his first televised address to the nation since that decision, Mr Pastrana warned Colombians to expect more attacks from the rebels.

"We should be prepared for the possibility that we will suffer bigger terrorist strikes. But we must have the dignity and strength to thwart them, united, until we are victorious against the intolerant few dedicated to destroying this country," he said.