MADRID — Spanish riot police said Thursday that the long hours they have been required to work this week to prevent protesters from gaining access to Madrid's main square "is not tolerable for much longer".

Over 200 police were deployed Thursday for the third straight day to close the Puerta del Sol square and prevent demonstrators angered over the government's handling of Spain's economic crisis from occupying it again.

Thousands of people set up camp in the square ahead of May 22 municipal elections to protest what they see as governments bowing to financial markets and ignoring the needs of ordinary people.

The vast ramshackle protest 'village' was dismantled on June 12 but members of the nationwide 15-M movement, named after its May 15 launch date, had since staffed a wooden information stand in the square round the clock.

But police cleared dozens of protesters who were camped at the information stand and along the central Paseo del Prado avenue in a dawn operation on Tuesday that resulted in no injuries or arrests.

Since then members of the movement, also known in Spain as the "indignants", have staged daily demonstrations where they try to gain access to the square but are blocked by rows of riot police backed by a helicopter.

The union representing Spain's riot police, SUP, on Thursday called on the interior ministry to "make a rational use of human resources, of police, because the schedule which riot police have had to put with, with long hours and no breaks, is not tolerable for much longer."

"And this is with a visit by the Pope on the horizon," it added in a statement.

Pope Benedict XVI will visit Madrid from August 18 to 21 to attend the Roman Catholic Church's World Youth Day celebrations which are expected to draw over one million pilgrims.

"We cannot go from allowing a shanty town to be set up for months to closing the square, diverting buses, closing the metro station and cordoning off the area," the police union statement added.

"There is a happy medium which would be allowing access to the square but not allowing tents to be set up."

The protesters have won broad public support in their fight against austerity measures, soaring unemployment and corruption-tainted politicians.

Polls show two-thirds of Spaniards sympathise with the indignants.