Millions of workers across crisis-hit Europe on Wednesday protested austerity policies with strikes and demonstrations.
Tens of thousands of protesters filled central Madrid. "The government is taking us to the abyss," trade union leader Candido Mendez said.
In Barcelona, where police estimated the number of protesters at about 100,000, participants threw bottles at riot police who responded with rubber bullets.
More than 100 people were detained throughout the country following strike-related incidents, the government said. More than 70 people were injured, including 43 police officers.
The daily El Pais estimated the number of Spanish protesters in the hundreds of thousands.
Protests also turned violent in Italy. In central Rome, police detained dozens of people and used armoured vehicles to confront angry protesters throwing bottles and stones.
Police officers were hurt in Turin - one seriously by protesters who smashed his anti-riot helmet - and in Milan and Padua, where two officers were hit by improvised fireworks.
Protesters blocked train stations in Naples and Palermo, ferry traffic in Genoa, and occupied an official building in Turin.
The European Trade Union Confederation (ETUC) had called "a day of action and solidarity" against austerity measures, recession and "dismantling the European social model."
Spain and Portugal spearheaded the protests with the first joint general strike on the Iberian Peninsula.
In Italy, left-wing trade union CGIL, the biggest in the country, called a nationwide strike and staged protests in 100 cities, drawing thousands of people. Controversially, other union groups did not join in.
Greek workers observed a three-hour strike, and some 5,000 demonstrators gathered in front of parliament in central Athens.
French unions also staged nationwide protests, while in Belgium, a rail employees' strike paralysed train traffic.
The Spanish strike affected rail and bus traffic and the Madrid underground. Unions put the general strike participation at 77 per cent, pointing to its impact in car and other factories. The government downplayed such figures, describing the strike day as "normal." Many shops remained open.
The strike had a bigger impact in Portugal. Bus and ferry traffic was irregular, few trains operated, and the Lisbon underground remained closed. Garbage was not collected, while many hospitals only offered emergency services.
Several incidents were reported, including the arrest of a Lisbon picket on charges of attacking a police officer.
Debt-ridden Spain and Portugal have drastically cut spending in attempts to cut their budget deficits. Unemployment has risen to 25 per cent in Spain and to 16 per cent in Portugal.
A rail workers' strike meanwhile largely paralysed rail traffic in Belgium, leading to the cancellation of several high-speed trains from Amsterdam to Paris. People travelling from France and Germany to Belgium had to take buses instead of trains.
The strikes also affected flight traffic. Some 700 flights were cancelled in Spain, as well as 80 per cent of flights at Lisbon airport.
Meanwhile, in Berlin, German Chancellor Angela Merkel said that the right to demonstrate was "fundamental to democracy," but that a case needed to be made to unions for austerity policies.
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