Mr. DeLaurentis (left) handed the letter to the Cuba’s interim Foreign Minister Marcelino Medina (source: bbc)
The US and Cuba have agreed to reopen embassies in each other’s capitals, a major step in re-establishing diplomatic ties severed in 1961.
Cuba said Havana and Washington will restore full diplomatic relations and open embassies on 20 July.
US President Barack Obama said the move showed that US and Cuban citizens were no longer “imprisoned by our past”.
Relations had been frozen since the early 1960s when the US broke links and imposed a trade embargo on Cuba.
But the two sides agreed to normalise relations at the end of 2014 and historic talks followed in April this year.
Since 1977, the US and Cuba have operated diplomatic missions called “interests sections” in each other’s capitals under the legal protection of Switzerland. However, they do not enjoy the same status as full embassies.
Underscoring the progress in the diplomatic relationship between the two countries, Mr Obama’s speech was broadcast live on Cuban television.
The president said there had been “very real and profound differences” between the US and Cuba, but admitted that the US had been “clinging to a policy that was not working”.
On Wednesday morning, the US’ top diplomat, Jeffrey DeLaurentis delivered a letter from the White House about restoring the embassies to Cuba’s foreign ministry.
It is the latest major milestone in a thawing process between the two countries’ relations, which started with secret negotiations and was announced last December.
In April, President Obama and his Cuban counterpart, Raul Castro, met for the first formal talks between the two countries’ leaders in more than half a century.
A month later, the US removed Cuba from its list of state sponsors of terrorism. Plans to resume ferry and air services between the US and Cuba were also announced.
Despite the new transport links, a Cuba travel ban is still in place for US citizens.
Cuba is also still subject to a US trade embargo which has been in place since 1962, though President Obama has urged Congress to lift it.
The US broke off diplomatic relations with Cuba in 1959 after Fidel Castro and his brother Raul led a revolution toppling US-backed President Fulgencio Batista. The Castros established a revolutionary socialist state with close ties to the Soviet Union.
In December 2014, the two presidents made a surprise announcement saying they would seek to re-establish diplomatic ties, ending more than 50 years of ill-will.