HAVANA, Cuba (AFP) — The Marine guard of the newly reopened US embassy in Cuba raised the flag over the building Friday for the first time in 54 years, marking the end of the countries’ Cold War standoff.

US Secretary of State John Kerry gave the cue to raise the flag, which was handed to the new contingent by the three retired Marines who had lowered the flag when Washington severed ties with Havana on January 3, 1961.

Kerry made the historic trip to Havana to formally reopen the US mission as a full embassy and set the seal on a remarkable rapprochement between the Cold War foes.

But he warned that Washington would continue to press Cuba’s communist government to pursue democratic reform as the countries normalise relations across the Florida Straits.

“The leaders in Havana and the Cuban people should also know that the United States will always remain a champion of democratic principles and reforms,” he said.

“We remain convinced the people of Cuba would be best served by a genuine democracy where people are free to choose their leaders with commitment, economic and social justice.”

The thawing in the Cold War conflict, begun in December by Presidents Barack Obama and Raul Castro, has been criticized in Washington by the US leader’s conservative opponents.

And in Cuba, dissidents have expressed concern that closer ties between the governments will leave them out in the cold.

But Kerry insisted the breakdown in ties and the US trade embargo on the island had failed to force Cuba to reform — and that a new path must be sought.

“There will be hiccups along the way but it’s a start,” Kerry told reporters travelling with him.