United States authorities on Sunday warned its citizens of potential threat of terrorist attacks in Europe, while Britain advised travellers of “a high threat of terrorism” in France and Germany.

The alerts follow media reports over the past week that U.S. and European intelligence agencies have uncovered and disrupted an alleged Al-Qaeda plot to carry out simultaneous attacks on major cities in Britain, France and Germany.

There was information to suggest that Al-Qaeda and affiliated organisations were planning such attacks, said the U.S. State Department in the travel alert.

The State Department also noted “the potential for terrorists to attack public transportation systems and other tourist infrastructure”.

Britain's foreign office, meanwhile, warned in the travel section of its website that attacks “could be indiscriminate, including in places frequented by expatriates and foreign travellers”.

Interior Minister Theresa May said Britain is facing “a real and serious threat from terrorism”, which was reflected in the country's threat level being set at “severe”, according to the Press Association.

French Defence Minister Herve Morin was also quoted Sunday by the daily Le Parisien as saying: “The terrorist threat exists, and could hit us at any moment.”

Media have focused on statements reportedly made under interrogation by Ahmed Siddiqui, a German detainee at a U.S. military prison in Bagram, Afghanistan. The attacks were to be carried out by Germans, Chechens and nationals of Arabic states, according to reports.

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