GENEVA (Reuters) - Switzerland said on Thursday it had no evidence of al Qaeda plans to attack next month's Euro 2008 football tournament, despite reported militant threats on the Internet.

La Liberte newspaper quoted Swiss security sources as saying they were taking seriously anonymous messages on Islamist Web forums before the June 7-29 event in Switzerland and Austria, one of which threatened to "transform the two safest European countries into hell".

Asked to comment on the report, Daniele Bersier, spokeswoman of the Swiss federal office for police matters, said: "Nothing has changed in terms of our analysis of the threat."

She said the two host nations were part of the "Western Europe threat zone" exposed to militant Islamist threats, and the world's third largest sports event "could well be a rewarding goal from the perspective of terrorists".

"However, it can again be stated that so far there is no evidence of concrete actions in preparation of an attack on Switzerland or Euro 2008," Bersier said.

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 Swiss host cities, and the authorities would react accordingly.

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.

(Reporting by Stephanie Nebehay; Editing by Mark Trevelyan)