Police fired tear gas at protesters who marched to the European Central Bank in Frankfurt, while in Spain and Portugal -- two of the countries that have received financial help -- more demonstrators filled the streets in angry marches.
"United against the troika. We don't owe, we won't pay," read some of the slogans brandished in Madrid.
The troika of international lenders -- the International Monetary Fund, the European Union and the European Central Bank -- have imposed strict conditions on countries such as Greece and Portugal in exchange for bailout funds.
In Spain they have overseen a bailout for the country's banks that has handed €40 billion ($52 billion) to the sector, angering protesters who say the money should help the poor.
Protesters say the belt-tightening measures applied by governments to meet the troika's conditions unfairly penalise the poor who suffer most from job cuts and tax hikes.
Several thousand demonstrators waving banners and red, yellow and blue Spanish republican flags marched along a central avenue in Madrid to the din of drums and horns to mass outside the European Commission .
"We are here fighting against the rulings of the troika, because we think they are governing only for the good of big capitalists, against the will of the majority of the people," said one protestor, Rafael Herguezabal, a 75-year-old retired bank employee.
He blamed the troika for policies introduced under pressure from Brussels, such as labour reforms, budget cuts and privatisations of public services, which Spain's government says are needed to stabilise public finances.
"Governments in Europe do what the troika tells them at the cost of impoverishing the working classes," Herguezabal told AFP.
Thousands of people also marched in Barcelona and organisers said similar protests were called in other countries including Greece.
In Lisbon protestors waved red cards outside the local offices of the International Monetary Fund, one of the architects of the country's €78 billion bailout two years ago.
"I am not responsible for others' mistakes," said one demonstrator in Lisbon, Manuel Oliveira, a security guard.
"It is not fair that some keep their privileges while the people have to tighten their belts."
Anger in Portugal was fanned by a new austerity plan announced in early May, which pushes back the retirement age to 66 from 65. It also cuts some 30,000 civil service jobs and lengthens working hours for civil servants.
In Frankfurt the march towards the European Central Bank (ECB) was halted several times because of police tear gas, but no injuries were reported.
"The policies of the European Central Bank and the troika ... are not the solution," said Roland Suss, a spokesman for the Blockupy movement that organised the Frankfurt demonstration.
Sixty-two-year-old Marica Frangakis from Greece, taking part in that march, said: "I'm from the baby boom generation, and we have had a relatively good life. But now we have to fight for our survival."
In Greece and Spain the unemployment rate has reached 27 percent, while Portugal's is forecast to climb to a record 18.2 percent this year.
Laying down its latest economic targets , the European Commission gave Spain, Portugal and several other countries more time to reach targets to cut their deficits.
Spain, which narrowly avoided a full-scale debt bailout last year, was given two extra years to bring its budget deficit below the limit of three percent of GDP by 2016.
Bailed-out Portugal got one year extra to 2015.