The agricultural sector can act as "a bridge" between Cuba and its old Cold War foe the United States, a visiting top US official said.

Agriculture Secretary Tom Vilsack is the third member of President Barack Obama's cabinet to visit the communist-run island after Secretary of State John Kerry and Commerce Secretary Penny Pritzker.

The trip is designed to speed up efforts at normalizing trade ties between Washington and Havana, after the neighbors agreed to restore relations in December after more than 50 years of highly tense ties including the Cuban missile crisis.

"I strongly believe that agriculture can act as a bridge between two peoples," Vilsack told a press conference.

"I'll be travelling back to Washington with the hopes to figure out over time how we, the United States, might have a more permanent presence here in Cuba.

"This visit is designed to begin the process of building a new relationship between the American people and the Cuban people."

While full diplomatic ties have been restored between the US and Cuba, the US economic sanctions in its trade embargo largely remain in place because the Republican-run Congress has to vote to end it.

US farm states are eager to boost their exports to the island. But the Americas' only communist state has very little access to credit, other than from allies China or Venezuela.