The US is now grappling with a new nightmare -- Europe's 'angry Muslims' eligible to travel visa free to the country by virtue of their being citizens of European countries, a senior official has said.

Terror networks span Europe from Poland to Portugal thanks to the spread of Islam among descendants of guest workers once recruited to shore up Europe's postwar economic miracle, Robert S Leiken, director of the Immigration and National Security Programme at the Nixon Centre, said.

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"In smoky coffeehouses in Rotterdam and Copenhagen, makeshift prayer halls in Hamburg and Brussels, Islamic bookstalls in Birmingham and 'Londonistan' and prisons of Madrid, Milan and Marseilles, immigrants or their descendants are volunteering for jehad against the West," writes Leiken in the July-August issue of  Foreign Affairs.

A militant, claimed Leiken, can cross Europe with little scrutiny. Even if noticed, he can change his name or glide across the border as counter-terrorism agencies remain reluctant to share sensitive information or cooperate on prosecutions.

The mass immigration of Muslims to Europe, said Leiken, was an unintended consequence of the post-World War II guest-worker programme.

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Today, Muslims constitute the majority of immigrants in most Western European countries, including Belgium, France [Images], Germany [Images] and the Netherlands and the largest single component of the immigrant population in the UK.

It is estimated that between 15 and 20 million Muslims now call Europe home and make up four to five per cent of the
population.