Relations between the US and Cuba have been frosty for decades
A senior American diplomat held high-level talks with the Cuban government during a visit to Havana earlier this month, US officials have confirmed.
It was the highest-level contact between the two sides in years.
State department official Bisa Williams held the talks with Cuba's deputy foreign minister.
The decades-old US trade embargo on Cuba remains, but there has been an easing of tension since US President Barack Obama came to power in January.
Earlier this month, Ms Williams, the deputy assistant secretary of state for Western Hemisphere affairs, was part of a US delegation that went to Havana to discuss the possible resumption of direct postal services between the two nations.
Direct services were suspended in 1963 and currently post must go through third countries, meaning it can take several weeks to arrive.
Ms Williams stayed on in Cuba after the postal service discussions for five more days, says the BBC's Michael Voss in Havana.
US diplomats say she also held separate meetings with a number of dissidents on the island.
US President Barack Obama earlier this month extended the 47-year-old trade embargo against Cuba.
Mr Obama has indicated he would be open to dialogue with Cuba's leaders.
But he has said that, like previous American presidents, he will only consider a full lifting of the embargo once Cuba's communist government makes significant moves such as the holding of democratic elections.
However, in a sign of thawing relations, he has eased travel restrictions for Americans wanting to visit Cuba and the two countries are holding direct talks on immigration.
Cuba's President Raul Castro has said he is prepared to negotiate with the Obama administration, providing there are no preconditions.
His brother, former President Fidel Castro, also last week praised Mr Obama for his commitment to tackling climate change.
But our correspondent says no-one is expecting any rapid breakthroughs on core issues such as ending the decades old trade embargo.
Instead both sides are looking at ways of working together on confidence building measures such as immigration and postal services and possibly anti-drug smuggling co-operation.
News of Bisa Williams extended stay suggests that this quiet diplomacy is starting to gather pace.