HAVANA — After more than a half-century of Cold War estrangement, the United States reopened its six-story embassy in Havana on Monday, and Cuba raised a flag outside its own stately embassy in Washington.

The resumption of diplomatic relations between the two nations — a historic milestone in the official thaw that President Obama set in motion last year — was the culmination of months of negotiations to overcome decades of enmity.

But the promise of restoring full ties remained remote. Even as top American and Cuban diplomats held a meeting at the State Department for the first time in decades, Cuba’s foreign minister railed against the United States’ travel restrictions, trade embargo and presence at the military base at Guantánamo Bay.

The Cuban official, Bruno Rodríguez, said those policies must end before the two countries could bring their grudge to a close, and lend “some meaning to the historic event that we are witnessing.”