The US State Department has issued a travel warning to Americans, over potential terrorist attacks in Europe. US officials, have promised to work closely with European countries to deal with the threats.

The US State Department says "current information suggests al-Qaida and affiliated organizations continue to plan terrorist attacks."

It also says public transportation systems and other soft targets could be vulnerable to attack.

Possible threats in Europe have spurred concerns among US and European authorities in recent days. One concern is there could be plots, similar to the deadly 2008 Mumbai attacks, where 9 gunmen went on a shooting rampage, killing more than 150 people.

The US department is urging its citizens to take every precaution, to "be aware of their surroundings and to adopt appropriate safety measures to protect themselves."

But US travellers in Paris didn't appear too worried by the recent developments.

An US tourist said, "The only thing I was afraid of was flights being cancelled, but apparently everything is running, pretty good, but I think it is a little bit exaggerated."

Speaking from Coliseum in Rome, another American tourist was similarly unfazed.

Another tourist said, "If I hear something like that and I get scared I think they have already won, so I just keep going."

While a US travel alert may hurt European tourism and dampen business travel, there is no strong opposition to the proposed alert from European leaders who privately have been advised of the impending action.

Hundreds of thousands of Americans travel to Europe at any given time, including tourists, students and business people. For insurance and liability reasons, many US college and university study-abroad programs will not send students to countries for which a warning is in effect.