Two leading Dutch politicians known for their critical views of Islam have been taken to safe houses by police after death threats were made against them following the murder of the filmmaker Theo van Gogh.

Van Gogh, the great-great grandnephew of Vincent van Gogh, was shot and stabbed in a "ritual killing" in broad daylight in an Amsterdam street on Tuesday, with his throat slit with a butchers knife, and a five-page letter stabbed to his chest with another knife.

It was the second murder of a public figure critical of Islam in the Netherlands, two-years after the anti-immigration populist Pym Fortuyn was shot by a left-wing activist.

Police announced today that they would prosecute under anti-terrorism laws van Gogh's suspected killer, a 26-year-old Dutch-born male of Moroccan ethnic origin named Mohammed B. It would make the killing the first recognised terrorist attack on Dutch soil.

Police have also arrested eight other Islamic radicals over the killing, and have connected it with the terrorist bombing in Casablanca.

Dutch leaders issued with the death threats since the murder include: Ayaan Hirsi Ali, a Somali refugee and former Muslim who is a liberal member of the Dutch parliament and high-profile critic of Islam; Geert Wilders, a right-wing populist opposed to Turkey joining the EU; the Immigration Minister Rita Verdonk, and Job Cohen, the Mayor of Amsterdam.

Ms Hirsi Ali and Mr Wilders have both been taken to safe houses by Dutch police. Dutch newspapers reported that police are worried that the threats – by telephone calls and e-mails - were evidence of a co-ordinated attempt by Islamic radicals to target politicians seen as "enemies of Islam".

The police released the note pinned to Mr van Gogh's chest, which was written in Arab and Dutch with phrases from the Koran, addressed to Ms Hirsi Ali.

It complained that the Netherlands was controlled by Jews, and called for jihad (Holy War) against infidels, America, Europe, the Netherlands and Ms Hirsi Ali. It said: "Islam will be victorious through the blood of martyrs. Only the death will separate the truth from the lies."

It was addressed to Ms Hirshi Ali, declaring: "Since you stepped into the political arena in the Netherlands you have been constantly busy terrorising Muslims and Islam with your remarks. With your apostasy you have turned your back on truth and you are marching with the ranks of evil."

Piet Hein Donner, the Dutch Justice Minister, said of the letter: "It is worrying because it gives the impression that it is not the message of an individual, but a wider organisation."

The killing has worsened already tense community relations in the Netherlands, with 30 people arrested for inciting hatred against Muslims. An internet book of condolences for Mr van Gogh had to be closed down because it became filled with 5,000 messages of anti-Islamic abuse.

Ms Verdonk recently announced that the Government would introduce a law to strip Islamic radicals with dual nationality of their Dutch passports.

There are nearly a million Muslims in the Netherlands, mainly from Morroco and Turkey, and the majority maintain dual nationality.

She said that the law would be changed "so that when a person is suspected of planning or involvement in extremism or serious crimes, we will take away their Dutch passport." Under separate proposals, imams will be required to teach about Dutch values in mosques.

Ms Verdonk said that the Netherlands had been "naïve" in failing to deal with deep divisions in Dutch society. "For too long we have said we had a multi-cultural society and everyone would simply find each other. We were too naïve in thinking people would exist in society together," she said.

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