The French President, Nicolas Sarkozy, has sent in police to clear barricaded fuel depots and restore supply as trade unions keep up their resistance to a pension reform due for a final vote this week.

Fuel imports have hit a record high, the government said, as it tried to get round a 24-day blockade of France's largest oil port, near Marseille, where 51 oil tankers lay idle in the Mediterranean, unable to dock.

With more than 3,000 petrol stations out of nearly 12,500 in France out of fuel, police could also be deployed to clear access to striking oil refineries, according to Sarkozy's order.

A nine-day transport strike in 2007 cost France about 400 million euros a day, according to the economy ministry, although analysts do not see the current strikes costing as much.

Economy Minister Christine Lagarde said that she could not estimate the full cost of the strike action for France but it was unlikely to have a major impact on gross domestic product if it did not last too long.

Lagarde said the government hoped petrol pumps would be full again in a few days, and urged people rioting on the fringes of protests or blockading fuel depots to think about France's image and its need to speed up its economic recovery.

The centre-right government has stood firm through a wave of anti-pension reform action since the summer but the most serious test of its resolve has been ongoing strikes that began last Tuesday at the country's 12 refineries and riots this week on the fringes of protests in Lyon and a western Paris suburb.