The head of the U.S. delegation that held a new round of migration talks with Cuba, said Friday that he had been able to visit Alan Gross, the American contractor serving a 15-year sentence on the Communist-ruled island after being convicted of subversion.

Edward Alex Lee, the U.S. acting deputy assistant secretary of state for Western Hemisphere affairs, told reporters that he saw Gross, though he declined to give details.

Lee said that during his migration talks with the Havana government, the United States again demanded Gross's release.

He also said that the Gross case is a key issue in America's approach to the island.

The case of Alan Gross constitutes one of the current stumbling blocks in relations between Cuba and the United States, at odds for over half a century.

Last month, Cuba said it was prepared for an "immediate" dialogue with Washington to find a solution to the Gross situation - but only on a "reciprocal basis," meaning that any negotiations would have to include the case of the four Cuban agents jailed in the United States for espionage.

As for the migration talks, Lee described the tone as frank and constructive.

He also noted as highly important for the Cuban people the migration reform that Havana put into effect a year ago and which eliminated the historic restrictions that blocked inhabitants of the island from freely traveling abroad.

He added that in the last fiscal year, the United States granted 32,000 visas to Cubans, 100 percent more than in the previous year.

Migration talks between Cuba and the United States are important political exchanges between two countries that have had no diplomatic relations since 1962.

Apart from that topic, Cuban and the U.S. maintain discussions of a technical nature about cooperation on matters like rescuing emigrants at sea and drug trafficking, Lee said Friday.

Alan Gross, now 64, traveled to Cuba on behalf of a Maryland company that won a contract from the U.S. Agency for International Development to expand Internet access and the flow of information on the Communist-ruled island.

Cuban authorities arrested him in 2009 in possesion of communications equipment.

Havana said he was illegally aiding dissidents and inciting subversion and in an August 2012 ruling, Cuba's highest court upheld the 15-year jail sentence imposed on the American.

Cuba has hinted that it would release Gross in exchange for the return of the four members of the "Cuban Five" intelligence agents who remain jailed in the United States.

Washington has dismissed talk of a possible swap, demanding that Cuba release Gross unconditionally. EFE