French troops enforcing the ceasefire in Ivory Coast have strongly condemned a helicopter attack by the government against a rebel-held village in the centre of the country.

This is a very serious incident Ange-Antoine Leccia French military spokesman

A French military source said Tuesday's attack - in which 11 civilians are said to have died - was "unacceptable" and would have "inevitable repercussions".

It is the first time the French have criticised either side since they agreed to maintain the fragile truce signed by the government and the main rebel group, the Ivory Coast Patriotic Movement (MPCI).

The statement came as another rebel group on Wednesday opened up a new front in the south-west of the country, close to the Liberian border.

The MPCI, who launched the civil war three months ago by trying to overthrow President Laurent Gbagbo, hold the Muslim-dominated northern half of Ivory Coast.

Rebuke

The French military says government helicopter gunships on Tuesday attacked the lakeside fishing village of Menakro, about 50 kilometres (30 miles) north of the ceasefire line agreed in October.

French troops sent to investigate say 11 civilians died and many others were wounded in the attack.

"People were shot like rabbits," a French soldier told AFP news agency.

The French say the attack was unacceptable and demanded an explanation from the Ivorian Government.

"This is a very serious incident," French military spokesman Ange-Antoine Leccia said.

The BBC's Paul Welsh in Ivory Coast says this is the strongest rebuke by the French since the war began.

Ivorian army spokesman Colonel Jules Yao Yao told the BBC that the raid was in retaliation for a rebel attack on government forces on Tuesday.

He said the French forces had been warned in advance that the government would be striking back.

French troops - who are in Ivory Coast to protect foreign nationals and enforce the ceasefire - insist they are neutral in the conflict.

Last week the head of French armed forces said any violation of the ceasefire line by either government or MPCI fighters would not be tolerated.

Rebels without a cause?

Meanwhile in the south-west of the country, fighting has erupted in an area previously untouched by the war.

The rebels want to overthrow President Gbagbo

Rebels belonging to another rebel group, MPIGO, say they have seized an oil palm plantation close to the Liberian border - 200 kilometres (120 miles) south of any previous fighting.

The plantation, in the village of Neka, is within a few hours' drive of San Pedro, the second biggest port in Ivory Coast and the route through which much of its valuable cocoa crop is exported.

The French say some of the attackers were from Liberia and appeared more interested in looting than in fighting for a cause.

Since new 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 near the town on Duekoue.

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