The Dutch government has vowed to take tough action against Islamic radicalism after the murder of a film maker.
Van Gogh directed TV series and wrote newspaper columns
Theo van Gogh, the director of a movie criticising the treatment of women under Islam, was shot and stabbed in Amsterdam on Tuesday.
Several men, all believed to be radical Islamists, have been arrested.
Dutch Deputy Prime Minister Gerrit Zalm promised more funding for intelligence services, and said terror suspects with dual nationality might be deported.
"We are going to ratchet up the fight against this sort of terrorism," he said.
"The increase in radicalisation is worse than we had thought."
The justice minister ordered certain government figures, MPs and Amsterdam's mayor to hire bodyguards.
Dutch prosecutors have said the chief suspect, known as Mohammed B, will face terrorism-related charges as well as a count of murder.
He is also expected to be accused of attempting to kill a policeman and a bystander.
"We will argue before the judge that he is at the centre of a criminal organisation and that the other arrested people are part of this group," said prosecutor Leo de Wit.
At least four others are expected to face charges, while two men have been released.
A letter threatens Ayaan Hirsi Ali, Van Gogh's scriptwriter
Dutch authorities say they found a letter signed by an unknown group on Van Gogh's body containing threats to kill the liberal politician Ayaan Hirsi Ali.
Ms Hirsi Ali is a Somali refugee who wrote the script to Van Gogh's controversial film Submission, which criticised Islam.
Van Gogh, the great-great-nephew of the 19th-Century artist Vincent van Gogh, received death threats after the film was broadcast on national television in August.
The authorities have said they are on alert for revenge attacks on Muslims.
Police are investigating whether several fires that broke
out on Thursday night at a mosque in the town of Utrecht were started deliberately.