French riot police prevented farmers from blocking freight access to the Channel Tunnel as protests against petrol prices continued to escalate.
Truck drivers in the dispute have been joined by Air France staff, who have blocked access to some terminals at Charles de Gaulle airport.
The European Commission, meanwhile, has given France 24 hours for information on whether the protests are obstructing the free movement of goods.
Protests gathered pace in France over high fuel prices after unions on Wednesday rejected proposals by the government to end a dispute that has caused severe disruption to the country's transport system.
Taxi drivers in Paris and other main cities also plan further strike action and demonstrations.
Lionel Jospin, the French prime minister, stepped into the dispute on Wednesday, warning that there would be no more concessions to interest groups after early attempts to appease protesters stoked the political crisis.
His move comes after two days of blockades by truck drivers caused fuel shortages and a run on petrol stations across the country.
Mr Jospin said the government would "not go any further" and there would be "no more negotiations", after striking road hauliers turned down the substantial tax cuts proposed on Tuesday night by Jean-Claude Gayssot, the transport minister.
Mr Gayssot's offer to reduce taxes on diesel fuel this year and freeze tax increases planned for next year were meanwhile attacked as "irresponsible" by the Green party, a member of the coalition government alongside the Communist party.
Trade associations representing the striking road hauliers said they would meet on Thursday to consider the implications of Mr Jospin's ultimatum. However, none of the associations called for a lifting of the blockade.
The strike, called on Sunday evening, came after similar action by fishermen last week forced the government to offer significant concessions. The truckers were then joined by other groups.
FNSEA, the main farmers' union, said on Wednesday that if the conflict with truckers was resolved, farmers would take over the blockades until they obtained similar concessions.
Mr Jospin urged the strikers to be "responsible" and accept the "major proposals" made by the government.
Analysts estimate that the concessions on offer account for FFr17,000 (1,580) a year for each truck.
Dominique Voynet, the Green minister of the environment, said the proposals would damage the government's efforts to bolster the train freight sector, and risked setting back the country's long-term environmental plans.
The increases in fuel taxes that Mr Gayssot offered to freeze were part of a seven-year plan, launched in 1998 by Ms Voynet, to bring diesel fuel prices in line with petrol.
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