As the Cuban flag rose over the embassy in Washington, D.C., some demonstrators gathered to show their support and opposition to repaired relations. (Jorge Ribas/The Washington Post)

The Cold War between the United States and Cuba officially ended Monday after 54 years, six months and 17 days, as the two countries restored diplomatic relations and reopened embassies in each other’s capitals.

The two governments made clear that they remain deeply divided on a number of issues, including Cuba’s demand that the United States lift its trade embargo and relinquish the American naval base at Guantanamo Bay.

“There has been no pulling of punches,” Secretary of State John F. Kerry said at a joint afternoon news conference after talks with Cuban Foreign Minister Bruno Rodríguez. Human rights improvements are among what Kerry said are “the things the United States would like to see happen” in Cuba.

But on a day steeped in symbolism, the two diplomats stood at the State Department before a row of three Cuban and three U.S. flags, addressed each other by first names and spoke in each other’s languages.

The path leading to the openings — marked with a festive morning reception at the Cuban Embassy in Washington and a quiet opening of doors at the U.S. Embassy in Havana — began in December, when President Obama declared that U.S. isolation of Cuba hasn’t worked and that a new policy of rapprochement was “the right thing to do.”

In brutal heat worthy of Havana, hundreds of invited guests gathered Monday morning on the sidewalk outside the elegant 16th Street mansion that served as Cuba’s embassy before relations were severed in 1961. A Cuban military honor guard attached Cuba’s red-white-and-blue banner with a single star to a newly installed flagpole and Rodríguez raised it as the Cuban national anthem burst from loudspeakers and morning commuters slowed to stare.

Among the invited diplomats, U.S. lawmakers, and activists were a number of Cuban Americans whose lives have been shaped by the long history of animosity between the two countries.

Ralph Patiño, a businessman and lawyer from Miami who was born in the United States after his father left Cuba before the revolution, donated the flag and said he’d like to retire on the island.

Diminutive Maria Brieva, 83, whose eyes welled as she struggled to see the raised banner from behind the crowd, left Cuba in 1962. She was on the first humanitarian flight that carried family members there in 1978, when she visited her mother for the first time.

Juan José Valdés, the geographer at the National Geographic Society, said being at the opening made him feel “closer to home.” He was 7 years old in 1961 when his parents sent him alone from Havana to this country. “For me, technically I can step on Cuban soil at the embassy,” he said. He took a picture of the new embassy plaque beside the door and posted it on his Facebook page.

“I would have walked from Miami for this,” said Sylvia Wilhelm, who came to this country as a child in the early 1960s and heads an organization devoted to building U.S.-Cuba bridges. “This is the culmination of so many years of hard work to change U.S. policy toward Cuba.”

Across the street, a small group of protesters began chanting “Cuba sin Castro” — Cuba without Castro — and some of those in front of the embassy shouted back “Viva Cuba” and “Fi-del, Fi-del,” in recognition of Cuba’s revolutionary leader. One voice yelled “Viva Raúl!” a mention of Fidel Castro’s younger brother, who has ruled since 2006 and agreed to the opening with Obama.

Inside, a massive, stained-glass skylight overlooked a formal staircase leading to the ­second-floor gallery of meeting rooms and offices. Another flag hung on the wall — the stained, somewhat tattered banner taken down more than a half-century ago when relations were severed. Initially kept in Miami by what Rodríguez called “a family of liberators,” it eventually made its way to a museum in the eastern Cuban city of Las Tunas, he said, “as a sort of premonition that this day would certainly come.”

In a room set up for a Rodríguez speech, both the Cuban and U.S. anthems were played. Rodríguez paid tribute to “the wise and firm leadership of Fidel Castro,” and to Washington, Lincoln and former U.S. president Jimmy Carter, who negotiated with Cuba over the opening of the quasi-diplomatic Interests Sections in the two then-shuttered embassy buildings under the diplomatic protection of Switzerland in 1977.

While full-fledged embassies are an important step, Rodríguez said, the challenge of establishing fully normal relations is “huge, because there have never been normal relations between the United States of America and Cuba.” In an example of the long memories Cuban officials often display in speeches about the United States, he recalled two U.S. military occupations in the early years of the last century, and the 1901 Platt amendment, which gave the United States the right to unilateral intervention in Cuba and an unbreakable lease to Guantanamo.

Most of the Platt provisions were repealed three decades later, but the U.S. claim to Guantanamo remains. At his news conference with Rodríguez, Kerry said that “we understand that Cuba has strong feelings about it, and I can’t tell you what the future will bring, but for the moment [Guantanamo] is not part of the discussion on our side.”

Although there is opposition in Congress, Obama has said he will push to lift the trade embargo. “What’s . . . going to make it crack is that Americans will ultimately find it ridiculous,” said Ben Rhodes, Obama’s deputy national security adviser. “It’s controversial in Washington, but not in the rest of America,” he said of eliminating the trade and banking restrictions that Cubans refer to as a “blockade.”

In Havana, the scene was much more subdued. Kerry plans to visit on Aug. 14 for a flag-
raising ceremony and celebration, but for the moment it was hard to discern any change. The new U.S. Embassy announced its existence on Twitter with a post that read “¡Hola amigos!” just after midnight.

At midmorning, about 150 people gathered, a few waving small American flags and others sporting Stars and Stripes T-shirts. One man held up a “Welcome USA” sign. But most just snapped photographs and stared at the blank glass-and-concrete facade.

In the small park a block away, hundreds of Cubans were lined up, as always, clustering in patches of shade and holding their visa applications.

Brian Murphy and David Montgomery contributed to
this report.