MADRID (Reuters) - Six people have been arrested in Spain, Britain and Germany accused of links to the Islamist militant group Islamic State, and the indoctrination and radicalization of potential members, the Spanish interior ministry said on Wednesday.

The arrests, organized by Spanish police in conjunction with police in Germany and Britain, detained four people in Palma de Mallorca, one in Britain and one in Germany, the ministry said.

The police forces from the different countries co-operated using European Union agencies set up to help share information related to fighting crime within member states - Europol, Eurojust and Sirene, the ministry said.

Those arrested devised and circulated videos with violent content and organized secret weekly meetings to recruit young people to travel to conflict zones to fight.

The police investigation began in 2015 after discovering a web page with a series of videos showing the indoctrination, capture and journey to Syria of a young Muslim resident in Spain.

The producer of the films, an ultra-conservative Salafi imam, was arrested in Britain as part of the operation. He was already under surveillance by several European countries, the ministry said.

He recently traveled to the Spanish Mediterranean island of Mallorca where he met the four arrested in Spain, urging them to capture and indoctrinate others, the ministry said. The man arrested in Germany had contact with the others and had taken part in recruitment videos made by the group.

Since Spain raised the security alert to level 4, the second highest, in June 2015, Spanish police have arrested 178 people accused of links to Islamist militancy.