A number of civilians were killed in the air strikes

Troops in the town, San Vicente del Caguan, erected banners on the field where Mr Pastrana's helicopter landed, promising not to let up in their war against the Revolutionary Armed Forces of Colombia (FARC).

The BBC's Peter Greste in Colombia says the president's visit had all the trappings of a pop star welcome, with thousands of cheering locals there to greet him.

For three years, the left-wing rebels have controlled the area the size of Switzerland, given to them when peace talks began more than three years ago.

Little resistance

But our correspondent says rebel resistance to the government offensive has been remarkably light, and the cheering villagers were expressing relief at the relatively trouble-free change of power.

Click here for a map of the former FARC safe haven

Mr Pastrana pledged not to abandon the town and said he would work for peace and stability.

But there are fears that right-wing paramilitaries will move into the area and kill anyone suspected of collaborating with the FARC, our correspondent says.

Mr Pastrana ordered the FARC out of the area after declaring the peace process dead, angered by the kidnapping of a senator on Wednesday.

Defence Minister Gustavo Bell has said the Colombian Government wants to show that FARC has been carrying out criminal activities within the area.

On Friday, government troops recaptured a former army base and moved on towards five towns inside the former rebel stronghold.

The troops have been moving in on foot

The head of the armed forces, General Fernando Tapias, said although rebel leaders had left the area, many fighters were disguising themselves and trying to mingle with civilians.

More than 100,000 people live in the area and it is feared that as fighting continues they could be caught in the cross-fire or forced to flee.

Neighbouring countries are braced for a possible refugee influx.

Town mayors in the zone have declared dusk-to-dawn curfews, and some are demanding that the government place international observers in the area to prevent right-wing paramilitaries from killing suspected collaborators.

"We're not guerrillas. We only had to live next to them," said the mayor of Mesetas, Maria Oliva Torres.