By Jason Webb

MADRID, June 12 (Reuters) - Spain promised "zero tolerance" for violence by striking truckers after police cleared picket lines blocking highways during a fuel protest.

The government said deliveries of food and other goods were returning to normal on Thursday after an agreement with most of the strikers on Wednesday although food distribution centres reported shortages and car factories remained at a standstill.

"The government is going to have zero tolerance for any act of intimidation or violence," said Socialist Prime Minister Jose Luis Rodriguez Zapatero, after incidents including an arson attack on a strike-breaking truck that left the driver with burns to 25 percent of his body.

The government said it had arrested 71 picketers for offences including intimidating non-striking drivers since the stoppage by 75,000 truckers began on Sunday night to call for government help to cope with high fuel prices.

The government, re-elected in March, tempted most truckers back to work with promises of tax breaks on Wednesday but has refused to accede to demands for minimum haulage charges.

Tax breaks were also offered by Portugal, which also negotiated an end to a truck strike on Wednesday.

However the scene at Madrid's main food market, Mercamadrid, which supplies the capital's shops and supermarkets, was far from normal on Thursday as the number of deliveries was reduced to a trickle because non-striking truckers were still being stopped by picketers.

Car plants were also at a standstill, due to a shortage of parts caused by the strike, national car makers' association Anfac said.

"There have been incidents on the highway. Some drivers some stopped because they're scared, and others have had to stop because they've slashed their tyres," Luis Alberto Carrion, head of the Madrid Fruit Association, told Reuters.

IMPACT ON ECONOMY

Riot police in body armour have broken up picket lines and the government has promised a police escort for working trucks.

In one incident, a driver working for a company which is not participating in the strike suffered burns to a quarter of his body after someone set his truck alight as he slept near where he had been trapped by a picket line.

The wife of another driver who was travelling in the cabin of a truck which arrived at Mercamadrid needed medical attention after picketers smashed the windscreen, Carrion said.

With fishermen already on strike and Madrid taxi drivers due to stop working for 24 hours from Friday, Spain is being hit hard by the protests caused by surging oil prices, which have spread elsewhere in Europe.

Spain's economy is already reeling from the global credit crunch and the collapse of a housing boom. Economic growth fell to 0.3 percent in the first quarter from 0.8 percent in the last three months of 2007, while inflation hit 4.6 percent in May.

Zapatero has been criticised by media and the conservative opposition for failing to do more to confront the strike and the economic slowdown.

"Whose fault is this? The state, the politicians. They promise so much," said Angela, a 62-year-old, shopping at Mostenses Market in central Madrid.

In the market, stalls seemed relatively well supplied, although some produce like tomatoes, oranges and peppers was running low.

And Fernando Martin, who owns a pork and beef stall, said the amount of meat he had on offer had halved.

"Three of four days more and we're screwed. In pork I've got practically nothing," he said. (Additional reporting by Ben Harding, Emma Pinedo, Robert Hetz and Axel Bugge in Lisbon)

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