France's finance minister said Monday that "very difficult" negotiations with Washington to settle a dispute over a tax on multinational tech giants were "far from being a done deal" as a self-imposed deadline loomed.

Paris commuters battled to reach work again on Monday as a 40-day-old strike dragged on and France's premier vowed "to go to the end" with the pension reforms that sparked the action.

French President Emmanuel Macron will on Monday host counterparts from five Sahel countries seeking more backing in the fight against a murderous jihadist uprising even as France's military role is being questioned.

Tens of thousands of demonstrators took to streets across France on Thursday in the latest mass protests against a pensions overhaul that critics say could cut benefits even while requiring people to work longer before retiring.

Tensions flared in Paris and other cities as some black-clad protesters smashed glass-panelled shopfronts and bus stops, while others hurled paving stones against police who tried to disperse crowds with tear gas.

French Prime Minister Edouard Philippe said Tuesday he had ordered police deployed at refineries and fuel depots to prevent planned union blockades amid the country's longest transport strike in decades.

France, it sometimes seems, is either in the throes of a major strike or facing the looming shadow of one. 

Workers in the country go on strike more than most nations in Europe. The current open-ended stoppages, which began on December 5, have halted most public transport in Paris and inter-city trains.

The boss of a hardline French trade union on Friday vowed to press on with a strike that has crippled transport in Paris for the past three weeks and is now the longest-lasting such action since the 1980s.

The French government and labour unions face off Wednesday over a pensions overhaul, 14 days into a crippling transport strike that is hurting businesses, wearing out commuters and casting a shadow over holiday plans.

The French government will unveil the details of a pension reform plan Wednesday that has already seen workers down tools in anticipation, crippling transport for a week as hundreds of thousands took to the streets in protest.

A speedy resolution appears unlikely, with Prime Minister Edouard Philippe warning Tuesday -- the sixth day of an open-ended transport strike -- of a lengthy battle ahead as unions vowed not to yield.

The most serious nationwide strike to hit France in years caused new weekend travel turmoil on Saturday, with unions warning the walkouts would last well into next week.

The challenge thrown to President Emmanuel Macron over his plans for radical pension reform has seen hundreds of thousands take to the streets and key transport services brought to a standstill.