After terror attacks on an airport and metro station in Brussels, the State Department in March issued a broad alert for travel across Europe that was slated to expire on June 20. On Tuesday, the State Department announced a new alert that expires on August 31: In its description, officials note that the large number of tourists visiting Europe this summer present "greater targets" for terrorists planning attacks in public locations, and urge U.S. citizens to exercise vigilance in public places or when using mass transportation.

The alert specifically references several key events: the Euro Cup, hosted in France June 10–July 10; the Tour de France, from July 2–24; and the Catholic Church’s World Youth Day, which will draw an anticipated 2.5 million visitors to Krakow, Poland, between July 26 and July 31.

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3/23/16: In the wake of twin terror attacks in Brussels, the State Department’s sweeping alert for travel to all of Europe is stoking visitors’ fears further—by raising the prospect of similar attacks in the near future. “Terrorist groups continue to plan near-term attacks throughout Europe, targeting sporting events, tourist sites, restaurants, and transportation,” the department said in its latest alert, issued shortly after the bombings at Brussels airport and a city metro station.

For the U.S. government to issue such a broad—and alarming—alert is unusual, but it’s not the only country recommending its citizens reconsider their travel plans. Several countries issued new advisories, such as Australia, which raised its alert for Belgium from "a high degree of caution" to "reconsider your need to travel."

So just how are would-be travelers expected to react to the barrage of alerts? While such a broad travel advisory to Europe would strike some as too vague, security experts said it was appropriate, given the circumstances. "With attacks all across Europe, it would be ill-advised to try and single out a specific country," says Edward Clark, senior security consultant for iJET International. The U.S. doesn’t warn against all travel, necessarily, but instead urges Americans to “exercise vigilance when in public places or using mass transportation.”

“Be aware of immediate surroundings and avoid crowded places. Exercise particular caution during religious holidays and at large festivals or events,” it said. That’s familiar advice to anyone who follows these travel advisories—and the warnings have come more frequently in the past six months following attacks in Paris, Turkey, and elsewhere. Whether it’s practical or useful is another question—after all, how do visitors completely avoid crowds? "While crowds are difficult to avoid, especially if on vacation, [you can] learn where to stand in the crowd and how to position yourself to limit your vulnerabilities," says Clark. "When you travel, select times when the airport is the least busy."

The State Department's alert does expire June 20, around the height of tourist season in several European countries; it's also a fairly typical three-month alert, and not as broad as the global alert issued in November following the Paris attacks.

Related: Why You Shouldn't Let Fear Get in the Way of Travel

This article has been corrected and updated. A travel alert, which was issued, is less acute and shorter term than a travel warning. Read on for more info.