Al Qaeda threatens to attack next month's Euro 2008 football tournament

Militants posted messages on Islamist web forums, threatening to transform Switzerland and Austria "into hell, like the hell in Iraq and Afghanistan".

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The championships, which begin on June 7, will be hosted in Switzerland and Austria which are in a "terrorist danger zone".

Juerg Buehler, a security expert with the Swiss federal police, said: "The Euro 2008 tournament is a potential target cited by the Islamist terrorist network."

Today Daniele Bersier, spokeswoman of the Swiss federal office for police matters, admitted the world's third largest sports event "could well be a rewarding goal from the perspective of terrorists".

But she stressed there was no concrete evidence of a planned attack at this stage.

She said: "Nothing has changed in our analysis of the threat.

"It can be stated that so far there is no evidence of concrete actions in preparation of an attack on Switzerland or Euro 2008."

She said the security picture would become clearer as the event approaches, including the potential for violence by rightist or leftist militants in the four host Swiss cities, and said the authorities would act accordingly.

The threatening messages were posted on 'sos minbar' and 'As-Sahab', two Islamist websites used by Al-Qa'eda and its followers.

Mr Buehler added: "We are taking these threats very seriously. We are on alert and we are following these Jihad forums very closely.

"It is through these that Osama bin Laden's agents awaken dormant cells.

"The situation is serious even if it is frustrated people hiding behind these sites."

Another message on one of the sites read: "The hour has come for fighters of the faith. They must make themselves heard" and "Austria must withdraw from Afghanistan."

A report by Swiss federal police in April said the neutral Alpine country was "not a primary target of Islamist terrorism, even if the jihadists consider it as a 'state of crusade'."

The report said that the uncovering of "sleeper cells" in Britain, Denmark and Germany in the past year had shown that "homegrown" Islamist terrorism existed in Europe.

But there was no evidence of preparations for an attack on Switzerland.

It said militant activities in Switzerland were mainly limited to propaganda, logistics and financing for groups active in Iraq and other hotspots.