France will be plunged into more strike chaos tomorrow with the threat of fuel shortages, street protests, and disrupted public transport and air travel.

Airlines were told to drastically cut back their flights into the country as the next round of protests over plans to raise the retirement age swing into action.

Meanwhile today oil workers defied a government's demand to get back to work amid the beginnings of panic buying at filling stations by motorists fearing diesel and petrol shortages.

Some reports said more than 1,000 filling stations, around a quarter of the total, had run out.

And short-haul flights from other European countries were warned to carry enough fuel for their return journeys.

Strikers have blockaded a dozen refineries and numerous oil depots in the last week as part of the widespread protests over president Nicolas Sarkozy's plan to raise the retirement age to 62, which the French Senate will debate on Wednesday.

They set piles of tyres on fire in front of a refinery at Grandpuits, east of Paris, after being hit with a legal order to reopen it.

Others formed a human chain to prevent the refinery workers from entering the plant.

Dozens of oil tankers remained stuck in the Mediterranean, anchored outside Marseille's two oil ports, where workers have been on strike for more than three weeks to protest a planned port reform as well as the retirement changes.

The government opened a crisis co-ordination centre in the Interior Ministry, focusing on the conflict in the oil sector.

Prime Minister Francois Fillon has pledged to do what is necessary to prevent fuel shortages, saying the government will not allow them to hurt the economy. The head of France's petroleum industry body said reserves were "enough to keep us going for a few weeks."

Jean-Louis Schilansky, president of the Petrol Industries Association, warned however that if the strikers continue to block fuel depots and if the nation's truckers join the movement, "then we will have a very big problem."

Truckers did take part in today's action, staging organised slowdowns forcing traffic to drive at a snail's pace on the main road between Paris and the northern city of Lille.

In Paris youths burned tyres and cars, set up blockades and clashed with riot police outside some schools.

Students from Lycee Joliot Curie in the suburb of Nanterre tried to blockade their school, with about 100 facing off against police, who responded with rubber bullets. In all, 261 schools were closed.

Rail unions, which have been on strike since early last week, have prolonged their walkouts throughout tomorrow to coincide with more than 200 street protests - the sixth in a month.

Union leaders also called for support strikes from other sectors, including energy, postal workers and private commerce, as well as from employees at Eurotunnel on the cross-Channel link to England.

France's DGAC civil aviation authority ordered airlines to cancel half of their flights tomorrow out of Paris' Orly airport, and almost a third at other airports nationwide, including Paris' largest airport, Charles de Gaulle. Most disruptions were expected to hit short- and medium-haul flights.

Airport operator ADP said strikes by oil workers at Charles de Gaulle had already begun causing some delays today.

Train traffic also continued to suffer from the nearly week-long strike. France's SNCF railway operator said about half its high-speed TGV trains had been cancelled today, but traffic on the Eurostar between Paris and London was normal.

Workers are angry because they consider retiring at 60 a pillar of France's hard-won social contract - and fear this is just the first step in eroding their often-envied quality of life.

Critics say Mr Sarkozy wants to adopt an "American-style capitalist" system and claim the government could find pension savings elsewhere, such as by raising contributions from employers.

The government points out that 62 is among the lowest retirement ages in Europe, the French are living much longer and the pension system is losing money already.

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