BERLIN — The German police announced Wednesday that they had arrested four men associated with the ultraconservative Islamic movement known as Salafism on suspicion of plotting to murder the leader of a far-right political party that has repeatedly taunted Muslims with caricatures of the Prophet Muhammad.

News of the arrests came as the federal authorities banned three associations linked to the Salafist movement in Germany, saying the groups were involved in recruitment, in fund-raising and in the distribution of propaganda over the Internet. The police raided the apartments of 20 people associated with the associations, known as DawaFFM, Islamische Audios and an-Nussrah the Interior Ministry said Wednesday.

The Salafist movement has been growing quickly here, attracting mostly young men, including Muslim immigrants and German converts, the authorities say. They believe the number of adherents has risen to about 4,500 from 3,800 over the past two years, as the movement has gained attention in clashes over the caricatures and a nationwide effort to distribute Korans.

The authorities have said videos and propaganda circulated over the Internet by DawaFFM helped radicalize Arid Uka, a young German originally from Kosovo who shot American airmen at the Frankfurt airport in 2011, killing two and injuring two others. Mr. Uka was later sentenced to life imprisonment.