ATHENS — Moving to drain power from one of the most violent rightist organizations in Europe, the Greek government conducted an extraordinary crackdown on the neo-fascist Golden Dawn party on Saturday, arresting 5 members of Parliament, including the leader of the group, and at least 15 other people.

A search was under way for another lawmaker and at least 10 more party members.

It is the first time that the leader of a political party and members of Parliament have been arrested in Greece since the fall of a military junta in 1974.

Less than two weeks ago, the murder of an anti-fascist Greek singer, the rapper Pavlos Fyssas, 34, ignited an uproar throughout Greece after the suspect claimed to be a Golden Dawn supporter.

The public outcry over the killing put substantial pressure on the government to move ahead with an investigation of the party.