Rebels in Ivory Coast have opened up a new front in the south-west of the country, after reportedly slipping over the border from Liberia.

Their attack puts them behind the positions of French troops who have been stopping a rebel advance.

In another development, the French news agency AFP reported that 11 civilians had been killed and several others wounded when a government military helicopter fired on a rebel-held village.

The rebels are being urged to lay down their arms

A French military official described Tuesday's attack on Menakro, a fishing village about 100km (60 miles) north of the capital Yamoussoukro, as "inadmissible and intolerable".

The three-month conflict has split the country between mainly Christian supporters of President Laurent Gbagbo in the south and west, and supporters of opposition leader Alassane Ouattara in the north who are largely Muslim.

The new front is 200km (120 miles) south of the existing areas of fighting and takes the war into an area of Ivory Coast which had not been affected until now.

The BBC's Paul Welsh, in Abidjan, says the rebels appear to have come across the Liberian border in the early hours of New Year's Day to attack a palm oil plantation, taking its vehicles and fuel.

People are leaving the area.

The rebels are now just 200km by road from San Pedro, the second biggest port in Ivory Coast.

In normal years, one-fifth of the world's cocoa, the raw material of chocolate, is shipped from there.

Since newer rebel groups first appeared in the west of the country a month ago, they have been saying they are heading to San Pedro and then on to the main city Abidjan.

That advance had been halted by French soldiers who set up positions to stop the western rebels moving deeper into government territory from where they originally appeared.

In a New Year's Eve speech to the nation, President Gbagbo again urged the rebels to lay down their arms.

But he has given no more details of a 10-point peace plan he is proposing despite having said he would present it to his people.