FRANKFURT, Germany (AP) — At least four police cars were set alight and two officers injured Wednesday as authorities confronted anti-austerity protesters trying to blockade the inauguration ceremony for the European Central Bank's new headquarters in Frankfurt, Germany.

Police said 350 people were detained. Protesters are targeting the central bank because of the its role in supervising efforts to restrain spending and reduce debt in financially troubled countries such as Greece.

German Justice Minister Heiko Maas said that "everyone has the right to criticize institutions like the ECB. But pure rioting goes beyond all limits in the battle for political opinion."

Several thousand riot officers pursued what they said was a minority of violence-minded activists using the protest as cover. The bulk of protesters conducted themselves peacefully, marching in groups, drumming and singing ahead of a rally in the city's main square. Some blocked bridges across the Main River or streets.

Police said one officer was injured by stones thrown near the city's Alte Oper opera house, several private vehicles were burned overnight, and several police cars were set on fire at a police station in the city center. Another police vehicle smoldered a block from the ECB.

Hundreds of officers ringed the ECB headquarters ahead of the inauguration ceremony.

The Blockupy alliance says activists plan to try to blockade the new headquarters and to disrupt what they term capitalist business as usual.

Some 10,000 people were expected for a rally in Frankfurt's main square, the Roemerberg. Participants were to include trade unions and Germany's Left Party.

The ECB, along with the European Commission and International Monetary Fund, is part of the so-called "troika" that monitors compliance with the conditions of bailout loans for Greece and other financially troubled countries in Europe. Those conditions include spending cuts and reducing deficits, moves that are aimed at reducing debt but have also been blamed for high unemployment and slow growth.

Anti-austerity activists received a political boost when Greece's Syriza party won elections there in January by campaigning against the bailout deal and its conditions, which they say has led to a "humanitarian crisis." Refusal of the conditions, however, has led to the withholding of further aid and the possibility of a chaotic debt default by the government.

ECB President Mario Draghi has called for more spending by governments that are in good financial shape, such as Germany — a call that has been mostly ignored by elected officials.

The ECB says it plans to be "fully operational" during the protest, although some employees may work from home.