WASHINGTON (Reuters) – The U.S. State Department warned Americans on Tuesday of the possible threat of terrorist attacks in Europe this summer, saying targets could include tourist sites, restaurants and large events such as the European Soccer Championship in France.

“We are alerting U.S. citizens to the risk of potential terrorist attacks throughout Europe, targeting major events, tourist sites, restaurants, commercial centers and transportation,” it said in a travel alert expiring Aug. 31.

“The 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.”

The travel alert noted that France will host the UEFA Euro 2106 soccer championship from June 10 to July 10 and that the French government had extended its state of emergency, imposed after the Nov. 13 Paris attacks that killed 130 people, through July 26 to cover the July 2-24 Tour de France bicycle race.

“Euro Cup stadiums, fan zones, and unaffiliated entertainment venues broadcasting the tournaments in France and across Europe represent potential targets for terrorists, as do other large-scale sporting events and public gathering places throughout Europe,” the department said.

It also said the Catholic Church’s World Youth Day event is expected to draw up to 2.5 million visitors to Krakow, Poland, between July 26 and July 31, saying local infrastructure may be strained by the large number of visitors to Poland.

“Poland will impose border controls at all of its national borders from July 4 to August 2, and visitors to Poland during this period should be prepared to show their passport and undergo stricter security screening throughout Poland,” it said.

(Reporting by Arshad Mohammed; Editing by James Dalgleish)