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A Somali-born member of Parliament who became an internationally known opponent of fundamentalist Islam said Tuesday she will resign and leave the Netherlands after the government said she was improperly granted citizenship.

Ayaan Hirsi Ali has been under police protection since a film she wrote criticizing the treatment of women under Islam provoked the murder of its director, Theo van Gogh, by an Islamic radical.

She said she had made the decision Monday night, after Immigration Minister Rita Verdonk told her "she would strip me of my Dutch citizenship."

"I am therefore preparing to leave Holland," Hirsi Ali told reporters in the Hague. She declined to comment on what she will do next, or on reports in the Dutch media that she will join the American Enterprise Institute in the United States.

Hirsi Ali falsified her name and date of birth on her asylum application when she arrived in 1992, fearing reprisals from her family after she fled an arranged marriage.

She was granted a passport in 1997 and acknowledged the falsification in 2002 during vetting as a candidate for parliament. There were no objections then.

But after a television program rebroadcast the matter last week, Verdonk ruled her naturalization had been improperly granted.

Dutch vice prime minister Gerrit Zalm, who was the leader of Hirsi Ali's VVD party in 2002, spoke at the same news conference and said he was "amazed at the speed" with which Verdonk's decision was made.

"If she reapplies for citizenship, I trust her application will be handled with the same urgency," he said.

Hirsi Ali became internationally known after the murder of van Gogh in November 2004. She wrote the script for his film "Submission," which criticized the treatment of women under fundamentalist Islam, and offended many Muslims.

Van Gogh's murderer left a note threatening Hirsi Ali, and she has been under continuous police protection since then. The Dutch state had been scrambling to arrange new housing for her after her neighbors in The Hague complained successfully last month that security arrangements for her had become an unbearable nuisance.

"It is difficult to live with so many threats on your life and such a level of police protection," Hirsi Ali said. "It is difficult to work as a parliamentarian if you have nowhere to live. All that is difficult but not impossible. It has become impossible since last night."

Supporters reacted with dismay to Hirsi Ali's downfall.

EU Competition Commissioner Neelie Kroes told Dutch newspaper Algemeen Dagblad that she was "ashamed of the Netherlands because a valuable person like Hirsi Ali is being shoved out of the country."

"She voiced her opinions in an un-Dutch way sometimes, but that was good for the debate," Kroes said.

Galen Irwin, a political science professor who mentored Hirsi Ali while she studied at Leiden University, said Verdonk's threats to strip the Somali-born legislator of Dutch citizenship were "strange."

"There is nothing new about Ayaan's perceived lies. What disturbs me is the fact that she told her party leadership about this in 2002" and they failed to act then, Irwin said.

Hirsi Ali said that she had been left with little choice but to resign while she resolves her citizenship problems.

"Instead of fighting for the issues I care about I would be getting into legal fights," she said. "It's better, more appropriate, more elegant to take the time for that than impose my own personal problems on the parliament and the public."