US State Department

US State Department issues travel alert for Europe

"While local governments continue counterterrorism operations, the Department nevertheless remains concerned about the potential for future terrorist attacks," the alert said. "U.S. citizens should always be alert to the possibility that terrorist sympathizers or self-radicalized extremists may conduct attacks with little or no warning."

VIDEO: Kerry at Havana flag raising ceremony

Cuban dissidents were not invited to the embassy ceremony, avoiding tensions with Cuban officials who typically boycott events attended by the country's small political opposition.

The US State Department said it had limited space at what it called a government-to-government event, and has invited dissidents to a separate afternoon flag-raising at the home of the embassy's chief of mission.