The UNHCR says most had run away from recent violence in Abidjan.

Aid agencies are said to be unable to reach parts of the west where forces loyal to disputed President Laurent Gbagbo have been losing ground.

France has circulated a draft resolution at the UN calling for sanctions against Mr Gbagbo.

This follows a call for UN sanctions and tougher action to oust him by West African leaders.

Mr Gbagbo is resisting calls for him to cede power to his rival, Alassane Ouattara - widely recognised as the winner of last year's election in the world's largest cocoa producer.

"The massive displacement in Abidjan and elsewhere is being fuelled by fears of all-out war," said UNHCR spokeswoman Melissa Fleming at the agency's headquarters in Geneva.

She pointed out that the estimate of up to a million displaced was double the figure from just a week ago.

Many of those fleeing are migrants from Ivory Coast's poorer northern neighbours, who went there looking for work when it was West Africa's economic powerhouse.

Some of Mr Gbagbo's supporters have accused the migrants and their descendents of backing Mr Ouattara and some have been singled out for attack.