By Brian Love

PARIS (Reuters) - Riot police clashed with demonstrators outside a school building in Paris on Wednesday, prompting government and police calls for an end to weeks of violent protests mainly linked to plans for a loosening of France's highly protective labor laws.

Police used tear gas to disperse a crowd that sought to stop them removing nearly 300 immigrants who had moved into an empty school building that is soon due to reopen for classes after renovation work, Paris police chief Michel Cadot said.

While the standoff had little directly to do with the contested government plans to make hiring and firing easier, some of the protesters came from a youth movement set up a month ago largely to demonstrate against those plans.

"The state is obliged to apply the law," Cadot said. The migrants from countries including Sudan and Eritrea were removed peacefully after police broke through a ring of 200 to 250 protesters, he added.

Four police were slightly hurt, a statement said.

A major police union, Alliance, said law enforcement forces were already working flat out to ensure greater security following last November's Islamist attacks in Paris and condemned what it described as mounting "anti-cop hatred".

Hundreds of police officers have been reported injured in the past few weeks in clashes with demonstrators across France, mostly during protest rallies against the labor law reform.

Seven riot police officers were hurt on Tuesday in clashes with masked youths in the western city of Nantes.

"This is totally unacceptable, with 300 police hurt since the start of the year," said government spokesman Stephane Le Foll. "We will not let this pass."

LABOR REFORM

The primary focus of protest is the planned reform of some of the most extensive and protective labor rules in Europe.

An Elabe opinion poll released on Wednesday showed three out of four French people oppose a bill that the government argues will slash red tape and encourage employers to recruit in a country where the jobless rate is above 10 percent.

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Critics fear the bill will undermine employers' obligations under the current national labor code.

The Alliance union urged police forces to stage their own demonstration on May 18 to highlight their plight.

Police chief Cadot is also seeking to tighten the noose on a rolling youth protest movement - called 'Nuit Debout' - that has been organizing late-night sit-ins at the large Place de la Republique square in central Paris.

After repeated clashes where youths hurled petrol bombs and paving stones at police, he has banned alcohol consumption and late night music on the square and told Nuit Debout activists to quit the area every day before midnight.

Nuit Debout says violent groups who are just looking for trouble have at times hijacked their protests. It also accuses the police of sometimes using heavy-handed tactics.

(Additional reporting by Simon Carraud; Editing by Richard Balmforth and Gareth Jones)