Havana ? Sen. Tom Harkin asked Cuban President Fidel Castro on Thursday to free 75 dissidents sentenced to long prison terms in the nation’s harshest crackdown in decades.

Harkin, who has fought for years to ease U.S. sanctions on Cuba, also urged Washington to adopt more moderate policies toward the island, promoting more openness between the two countries while emphasizing respect for human rights.

Sen. Tom Harkin of Iowa, who has fought for years to ease American sanctions toward Cuba, on Thursday called on the island's leaders to free 75 dissidents sentenced to long prison terms.

Harkin and Castro “had a frank, cordial conversation about human rights, trade and other issues that relate to both countries,” the senator’s Washington office said in a statement.

The senator demanded the release of the dissidents, his office said.

Harkin, D-Iowa, was the first American senator to visit Cuba since Castro’s government began its mass roundup of opposition leaders in mid-March.

“Some said I should not come here under these circumstances,” Harkin told reporters Thursday before leaving Cuba. “But a policy of isolation and the embargo of 42 years has not achieved any U.S. objectives nor made life any better for the average Cuban citizen.”

Cuban prosecutors tried the dissidents in hearings that lasted no more than one day each. They were sentenced to prison terms ranging from six to 28 years.