Fifteen people were arrested and 39 people injured overnight in central Madrid, police said, after tens of thousands of people took part in a protest against the government's latest austerity package.
Police fired rubber bullets to disperse groups of protesters in streets in and around the Spanish parliament building.
The protesters set fire to rubbish bins and threw cans and other objects at police
A spokeswoman said today that 10 police officers were among the injured.
The demonstration in the capital was one of 80 held in cities across Spain to protest against the austerity measures the conservative government says are necessary if Spain wants to avoid a bailout like Greece, Ireland and Portugal.