Petrol shortages caused long tailbacks of motorists in parts of France Monday, as protesters angry over government labour reforms blockaded some of the country's oil refineries and fuel depots.

The action was the latest in three months of strikes and protests against the draft law that has set the Socialist government against some of its traditional supporters and sometimes descended into violence.

Some 1,500 petrol stations out of a total of 12,000 across France have either run out of petrol or are close to running dry, said Transport Minister Alain Vidalies.

The northwest of the country was worst hit over the weekend. As deliveries dwindled, drivers were forced to seek out petrol stations that had not run out of fuel.

But authorities said the situation was exacerbated by some motorists rushing to stock up because they feared supplies were about to run out.

Local authorities in some regions imposed rationing to eke out the supplies and police moved in to access some refineries and fuel depots blockaded over the weekend.

"Five out of eight French refineries are on strike, at a halt or in the process of shutting down," an official from the CGT union, Emmanuel Lepine, told AFP.

- Burning tyres -

Another CGT official, Eric Sellini, said activists had blockaded 189 fuel depots for several days, though police had since cleared the protesters from some of them. He was unable to say how many were still blocked.

To add to the disruption, tailbacks were building up at those stations still open, slowing traffic on the surrounding roads.

In the cities of Nantes, Rennes and Brest in the northwest, motorists were waiting up to an hour to get to the pumps.

In the southeast, union activists blocked a road leading to the Fos-sur-Mer refinery with burning tyres.

And in Donges, near Nantes, on the northwest coast, union activists used wooden pallets and burning tyres to block access to a fuel depot there.

But France's Socialist government has made it clear it will stand by the controversial labour reforms.

Speaking during a visit to Israel on Sunday, Prime Minister Manuel Valls condemned the blockade of the fuel depots and said the authorities would keep working to lift them.

"I'm asking everyone to face up to reality, not to put the country's economy in difficulty and to respect the users," Valls told BFMTV.

- Labour reforms 'will be passed' -

He was defiant about the labour market reforms.

"The labour law will go to the end of its parliamentary passage," he told BFMTV.

Finance Minister Michel Sapin denounced the attitude of the CGT union.

It was perfectly acceptable to protest against a proposed law or to make political demands, he said. "But there is a certain point... at which the action becomes illegitimate," he told iTELE.

The government says the changes contained in the draft labour law will make France's notoriously rigid labour market more flexible and create jobs.

The government forced the bill through the lower house of parliament earlier this month without a vote.

Opponents say the reforms will erode job security and do little to bring down the unemployment rate, stuck at 10 percent and nearly 25 percent for young people.

The proposed law has led to months of strikes, protest marches and demonstrations.

Last week, train drivers and air traffic controllers walked off the job, causing cancellations across the country.

Many of the rallies and demonstrations have ended in confrontation between masked youths and riot police.

Over the past two months, some 350 members of the security forces have been injured during demonstrations.

Much of the unrest has been blamed on small groups of troublemakers who appear bent on targeting the security services.