The U.S. State Department has issued an alert for Americans travelling in Europe, warning them there is a greater potential that al-Qaeda might launch attacks against U.S. citizens and Europeans.

Authorities are concerned that militants may be planning co-ordinated attacks similar to the Mumbai shooting rampage in 2008.

The alert urges U.S. citizens to be extra vigilant when they're in public places such as tourist spots and transportation hubs.

It does not focus on any particular areas of Europe, but Britain's Foreign Office mentions France and Germany in an upgraded travel advisory for its citizens. The British government said the threat of terrorism in those countries is considered "high." Before Sunday's change, the threat level was deemed "general."

Following the U.S. alert, the Department of Foreign Affairs urged Canadians to be vigilant while travelling in Europe. Canadians there should be aware of their surroundings, monitor local news reports and follow the advice of local authorities, said the agency, which is closely monitoring the situation in Europe.

It also encouraged Canadians to regularly consult the government travel website for updated information and to register with the Registration of Canadians Abroad service in order to receive the latest advice.

The U.S. travel alert is a cumulative result of information the United States has received over an extended period, an official said.

State Department spokesman P.J. Crowley declined to comment Saturday on the matter. But he said the administration was focused on al-Qaeda threats to U.S. interests and would take appropriate steps to protect Americans.

U.S. and European security experts have been concerned for days that terrorists may be plotting attacks in Europe with assault weapons on public places.