The State Department singled out the tournament in France
The US State Department has issued a "potential terrorist attacks" warning for Americans planning to travel to Europe for events such as the Euro 2016 football tournament.
"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 states.
The State Department singled out the Euro 2016 tournament, which is being hosted by France between 10 June and 10 July.
"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 alert said.
It also warned travellers planning to attend the Tour de France, which runs through 24 July.
France already extended its state of emergency - imposed after the 13 November Paris attacks - through 26 July.
The Statement Department warning also noted the Catholic Church's World Youth Day event between 26 July and 31 July in Krakow, Poland.
US citizens are being told to "exercise vigilance" in public spaces or while using public transportation, and to "avoid crowded places".
The Europe travel alert is set to expire on 31 August.
The State Department said US authorities are working "closely with our allies and will continue to share information with our European partners that will help identify and counter terrorist threats".