Americans in Europe, and those with plans to visit, were given a warning by the US State Department yesterday to "take every precaution" because of the elevated threat of terrorist attacks that could be aimed at popular tourist spots as well as transportation hubs.

After the alert was issued early yesterday morning in Washington DC, British Home Secretary Theresa May said it was consistent with the British view of the threat. The Foreign Office warned of a "high threat" of attacks in countries including France and Germany.

The warnings come after several days of media reports, partly confirmed by government sources, of new intelligence suggesting that attacks in Europe may be imminent and may resemble the 2008 commando-style assaults in Mumbai, India, that left more than 170 people dead.

No individual countries were singled out in the American alert. Officials noted also that there were still no plans last night for the US administration to issue a more grave travel "warning", which would explicitly encourage Americans to stay away from European destinations. The purpose of the alert, they said, was to ensure vigilance.

"US citizens are reminded of the potential for terrorists to attack public transportation systems and other tourist infrastructure," the State Department said. "Terrorists have targeted and attacked subway and rail systems, as well as aviation and maritime services."

Almost simultaneously yesterday, the Foreign Office upgraded its travel advisory about France and Germany, telling Britons that the threat of terrorist actions in those countries was considered high. Previously, the risk in Germany and France had been pegged as "general" by London.

It seemed clear that the changing language of the travel advisories had been closely co-ordinated on both sides of the Atlantic. "The terrorist threat exists, and could hit us at any moment," the French defence minister, Herve Morin, said in an interview in the newspaper Le Parisien. "Networks organising themselves to prepare attacks are constantly being dismantled around the world. It is good for the French to know this." The French police again closed the Eiffel Tower briefly last week because of unconfirmed threats against it.

The intelligence seems to have been gathered in part from a German national held at Bagram Air Base in Kabul. He is 36-year-old Ahmed Sidiqi of Hamburg who, according to officials, received training in firearms and explosives at terror network camps in the Waziristan region of north-west Pakistan. Other sources have spoken of eight Germans and a pair of British brothers involved in a plot. US officials are said to believe that the new activity has been launched at the direction of Osama bin Laden.

The warning to US citizens said terrorists "may elect to use a variety of means and weapons and target both official and private interests". It went on: "US citizens should take every precaution to be aware of their surroundings and to adopt appropriate safety measures to protect themselves when travelling."

Following Theresa May's comments, the threat level in the UK remains the same at "severe", meaning the Government considers an attack highly likely.