By William Horsley The BBC's European Affairs correspondent

The killing of the controversial right-wing Dutch politician Pim Fortuyn has caused deep shock well beyond the borders of the Netherlands.

Although there was no immediate evidence about the motives for the shooting, it came shortly before scheduled elections, and has the hallmark of a politically-motivated assassination.

Such incidents have been thankfully rare in recent times

Even though he was a newcomer to politics and his anti-immigrant views and well-known criticisms of Islam were widely seen as provocatively right-wing, Pim Fortuyn was undoubtedly a politician with a big following.

Some thought he might even be a future leader of the Netherlands.

The killing of such a prominent figure has shocked and horrified people everywhere.

Political killings

Such incidents have been thankfully rare in Europe in recent times.

Organised politically-motivated campaigns of violence have indeed claimed many lives - in the case of both the continuing campaign by the Basque separatists of ETA in Spain and, until the truce in Northern Ireland, the sectarian conflict between Irish republican and Ulster loyalist paramilitary fighters.

Jean-Marie Le Pen got to the last round of the French elections

But otherwise, extreme acts of violence against any person for their political views have been few and far between.

Among such cases, the motive for the shooting of Swedish Prime Minister Olaf Palme in 1986 was never explained.

Near-fatal assaults in 1990 on two German politicians, Oskar Lafontaine and Wolfgang Schaueble, seemed to reflect the turbulent times after German re-unification, but were the acts of mentally disturbed individuals.

Rising tensions

The shooting of Pim Fortuyn seems to be something new - an assault on one of Europe's most successful figures in the new far right-wing movement.

It will raise the political tensions not only in the Netherlands, in its current election campaign, but potentially in many parts of Europe - where issues of immigration, race relations and nationalism have come to the centre of the political debate.

In recent months, Jewish, Muslim and other minority communities have complained of feeling threatened in France and other countries.

Against that, Jean-Marie Le Pen's National Front made its political breakthrough by voicing fears about mass immigration and claiming that those in power have tried to silence their complaints.

Quick and effective action to find and prosecute those responsible for Pim Fortuyn's death is essential in the face of this sudden threat to peaceful politics.