Members of a German far-right group arrested last week are believed to have been plotting “shocking” large-scale attacks on mosques similar to the ones carried out in New Zealand last year, a government spokesman has said.

Investigations into 12 men detained in police raids across Germany on Friday had indicated they planned major attacks, officials said, following weekend media reports that the group aimed to launch several simultaneous mass-casualty assaults on Muslims during prayer gatherings.

“It’s shocking what has been revealed here, that there are cells here that appear to have become radicalised in such a short space of time,” the interior ministry spokesman Björn Grünewälder told reporters at a Berlin press conference.

Angela Merkel’s spokesman Steffen Seibert said: “It is the task of the state, and of course of this government, to protect free practice of religion in this country, with no reference to what religion it might be.

“Anyone practising their religion in Germany within our legal order should be able to do so without being endangered or threatened.”

Media reports said the group planned to use semi-automatic weapons to mimic last March’s attacks in Christchurch, New Zealand, in which 51 people were killed at two mosques.

The alleged leader of the group, which was known to the authorities and whose meetings and chat activity had been under observation, had detailed his plans at a meeting organised with his accomplices last week.

Investigators learned about it from a person who had infiltrated the group, the reports said.

Prosecutors said on Friday they had launched raids to determine whether the suspects already had weapons or other supplies that could be used in an attack.

German authorities have increasingly turned their attention to the country’s underground extreme-right scene since the murder of the conservative local politician Walter Lübcke last June, and an October attack on a synagogue in the eastern city of Halle.

Der Spiegel reported that police list 53 people belonging to the extreme right as “dangerous” individuals who could carry out a violent attack.