The US State Department says targets could include major events, tourist sites, restaurants and commercial centres.
The United States has issued a warning to American citizens visiting Europe this summer to be on the alert about the potential threat of attacks.
The State Department said on Tuesday targets could include major sporting events and tourist sites, as well as restaurants, commercial centres and transportation.
“A large number of tourists visiting Europe in the summer months will present greater targets for terrorists planning attacks in public locations, especially at large events,” it said.
“We are alerting US citizens to the risk of potential terrorist attacks throughout Europe, targeting major events, tourist sites, restaurants, commercial centres and transportation.”
The Euro 2016 football championship, which runs from June 10 to July 10, is being held in France, which is in an extended state of emergency following last year’s deadly attacks in Paris.
Another major event held in the country is cycling’s Tour de France, while millions of people are expected in Krakow, Poland, for the Roman Catholic Church’s World Day in late July.
Correspondent Alan Fisher, reporting from Washington DC, said this was “a standard warning from the State Department ahead of what it could become a very busy summer”.
“They are saying ‘look, if you’re travelling to any of these events, if you’re moving around Europe, please be aware of the risks involved,” he added.
“Clearly, given the big summer of sport that is coming up in Europe and concerns with recent incidents in Belgium and France, there is heightened concern.”
The State Department warning expires on August 31.