Rebels in Ivory Coast claim to have seized a town after a fierce battle in the country's volatile west near the border with Liberia, panicking tens of thousands of refugees who had already fled violence over a deepening political crisis.

The New Forces rebels said in a statement on their website that they seized Toulepleu on Sunday.

The statement said: "The large town of Toulepleu in the west of Ivory Coast is now in the hands of the army of the New Forces (rebels) since Sunday at noon following an intense combat."

The town was the scene of heavy fighting on Sunday between forces backing the political rivals who both claim to be Ivory Coast's president. The rebels are backed by the UN-recognised president, Alassane Ouattara. Government forces are allied with former president Laurent Gbagbo, who is refusing to leave office.

Saah Nyuma, the deputy director of the Liberia Refugee Repatriation and Resettlement Commission, said he heard the sounds of explosions coming from Ivory Coast. At least one mortar shell fell on the Liberian side of the border on Sunday.

Analysts fear that Ivory Coast's political crisis following a disputed presidential election will spill over into full-blown civil war.

Nearly 400 people have been killed since the 28 November vote, according to a UN and an Associated Press tally of bodies. The UN refugee body says more than 200,000 people have fled fighting in the main city of Abidjan in the last week, and more than 70,000 have crossed the border into Liberia to avoid the fighting.

The UN has declared Ouattara the winner, but Gbagbo refuses to cede power after more than a decade in office. His security forces are accused of abducting, torturing and killing political opponents.

Over the weekend, gangs of young people aided by uniformed police ransacked at least 10 houses in Abidjan belonging to officials allied with Ouattara.

"They're trying to install an atmosphere of terror," said top Ouattara adviser Amadou Coulibaly. "But you can't do more than what they've already done, firing on unarmed women. They're getting desperate."

Governments around the world swiftly condemned Thursday's killings of six female demonstrators.

Britain's minister for Africa, Henry Bellingham, said he was "deeply concerned" about the deteriorating security situation in Ivory Coast and was "appalled" to hear that women were killed during a peaceful demonstration.

"This is a deplorable and cowardly act against unarmed protesters calling for the results of the presidential elections to be respected," he said. "Gbagbo's continuing refusal to cede power ignores the will of the Ivorian people, challenges African democracy, and risks further violence and instability."