HAVANA — Jubilant crowds waved American flags and chanted “Long live the United States!” as the Stars and Stripes rose over the newly reopened U.S. Embassy in Cuba on Friday after a half-century of often-hostile relations. Secretary of State John Kerry celebrated the day but also made an extraordinary, nationally broadcast call for democratic change on the island.

Hundreds of Cubans mixed with American tourists outside the former U.S. Interests Section, newly emblazoned with the letters “Embassy of the United States of America.” They cheered as Kerry spoke, the United States Army Brass Quintet played “The Star-Spangled Banner” and U.S. Marines raised the flag alongside the building overlooking the famous Malecon seaside promenade.

Meeting more than 54 years after the severing of diplomatic relations, Kerry and Cuban Foreign Minister Bruno Rodriguez set an early September date for the start of talks on full normalization of a relationship so long frozen in enmity.

Not all the talk was as warm as the sunny summer day. Kerry and Rodriguez said their nations would continue to disagree over issues such as democracy and human rights. But they also said they hoped to make progress on issues ranging from maritime security and public health to the billions of dollars in dueling claims over confiscation of U.S. property and the U.S. economic embargo on the island.

It seemed that virtually all of Cuba was glued to television or listening by cellphone as Kerry directly addressed the island’s people on political reform. That’s a subject that has remained off-limits in Cuba even as the single-party government has implemented a series of economic reforms and re-established diplomatic ties with the U.S.