Spain's "indignados" gathered again in the city's emblematic Puerta del Sol on Sunday to protest against what they saw as excessive violence when riot police cleared the square of a previous demonstration early in the morning.

The version of events given by those in the square when it was cleared at 5am contradicted that of Spain's interior ministry, which claimed dozens of protests around Spain had ended "without incident".

Press photographers were among those expelled from the Puerta del Sol as police chased protesters around nearby streets.

Javier Bauluz, part of a team of Pulitzer prize-winning photographers from AP, was pushed and struck in the face by a police officer, according to fellow photographer Gabriel Pecot . At least one photographer working for an international press agency was among those ejected from the square.

"The general attitude was to get us out of the square and prevent us from working, shoving us if necessary," said Pecot.

Protest co-ordinators said about 20 people were injured at the end of the first of a series of demonstrations to mark the first anniversary of the avowedly non-violent indignado movement.

Police reported that two of their number were hurt and 18 people arrested – though many more reportedly face administrative fines after having their details taken down.

"The violence used was disproportionate," said an indignado spokeswoman. "People were having a very calm assembly when police came in."

The indignados began protesting last year against the political system as a whole and have since moved on to fight health and education cuts, bank bailouts, mortgage foreclosures and austerity measures that have pushed Spain back into recession.

The conservative government of Mariano Rajoy has vowed not to allow the indignados to repeat the camp-outs that were tolerated by the previous socialist government.

The interior ministry did not respond to queries about the allegations from the Guardian.

With protests called for Monday and Tuesday as well, the situation looked set to remain tense for two more days. It was not clear whether protesters planned to stay again all night, a move that would almost certainly see riot police return.

"I imagine this is something that the various open assemblies being held this afternoon will debate," the spokeswoman said.

The atmosphere contrasted with Saturday's massive demonstration, which saw the Puerta del Sol packed with demonstrators, including families with young children on their shoulders and a group of pensioners that called itself the Indignant Grandparents.

Rajoy's government is wary of the indignados and their protests, especially with financial markets jittery about the state of the country as it falls back into recession, unemployment reaches 24%, bond yields rise and the country's fourth largest bank, Bankia, is nationalised. A poll in el País newspaper on Sunday showed that 51% of Spaniards still sympathised with the movement, though this had fallen from 64% a year ago. © Guardian News and Media 2012

Photo of May 12 demonstrators by Alejandro Garcia Montoro via Flickr