Roughly 30 people burst into the cathedral of St Gregory Palamas and, aside from interrupting the service, "destroyed what they could", a spokesman said.

The cathedral is named after a 14th-century archbishop of Thessaloniki who is revered in the Eastern Orthodox Church.

Police say those arrested included 19 men and seven women. Seventeen are Greek, with the rest from Germany, the UK, Austria, Switzerland and Morocco.

The anarchists were protesting against a police operation on Wednesday in the city in which anarchists and refugees were evicted from three illegally occupied buildings.

One of the buildings, formerly an orphanage, is the property of the Greek Orthodox Church and is being demolished to make way for a new hospice.

Police arrested 74 anarchists in that operation, 64 of them foreigners. The 33 refugees were later released.

Before dawn on Sunday, an improvised device exploded outside the offices of the construction company hired to demolish the church's property, but caused little damage.