Cuban President Raul Castro on Wednesday demanded an end to the U.S. embargo against his country in order to make progress in talks to normalize relations.

"The main problem has not been resolved: the economic, commercial and financial blockade, which causes huge human and economic damage and is a violation of international rights," Castro said.

American Express said Wednesday that it plans to launch services for its credit card users in Cuba, after Washington and Havana agreed to establish relations following a half-century feeze.

Moving in the steps of rival MasterCard, an American Express spokeswoman said the company had plans to begin business activities in Cuba, "consistent with the president's announced policy change," though no specific date for a launch is set.

The United States welcomed Tuesday former Cuban leader Fidel Castro's belated response to the thaw in ties between the Cold War foes as a sign that change is underway in Havana.

"We take his reference of 'international norms and principles' as a positive sign," State Department spokeswoman Jen Psaki told reporters, after Castro's letter was released.

Cuban leader Fidel Castro has broken his silence on a historic rapprochement between Washington and Havana, implicitly endorsing it even as he expressed an abiding distrust of his old foe.

The 88-year-old revolutionary icon had said nothing since last month's surprise agreement, raising questions not only about where he stood on mending relations with Washington, but also about his health and political status.

Alfredo Castellano travels half an hour to Havana twice a week to write emails in a computer center with a Fidel Castro poster outside and aging machines inside.

Like most Cubans, he lacks Internet access at home, but many hope this will change after the United States offered to bolster the communist island's tightly-controlled telecommunications as part of a historic diplomatic detente.

Fidel Castro does not "trust the U.S., nor have I spoken with them," the revolutionary icon, 88, said in a letter attributed to him and read out on state television Monday.

"That does not represent -- far from it -- a rejection of peacefully settling conflicts," said the letter, a week after communist Cuba and the United States held landmark talks in Havana as they attempt to normalize ties.

Pentagon chief Chuck Hagel said it is "going to be very difficult" to close the controversial U.S. prison at Guantanamo Bay by the end of President Barack Obama's term in two years.

In an interview with National Public Radio that aired Monday, Hagel also acknowledged that he had taken a cautious approach to approving the transfer of some detainees out of the prison, which had reportedly irritated some officials in the White House.

MasterCard in March will begin processing transactions made on U.S.-issued cards in Cuba, becoming the first major credit card company to do so since Cuba and the United States started to normalize relations.

MasterCard said in a statement Friday that the move, effective March 1, follows renewed guidance from the U.S. Department of Treasury's Office of Foreign Assets Control.

The highest-ranking U.S. official to visit Cuba in three decades met with leading dissidents on Friday, but one prominent opposition figure stayed out amid differences over Washington's rapprochement with Havana.

Roberta Jacobson, the State Department's top official for Latin America, met with seven government critics under crystal chandeliers at the lavish mansion of the head of the U.S. Interests Section in Havana.

The highest-ranking U.S. official to visit Cuba in 35 years met with leading dissidents on Friday, but one prominent opposition figure stayed out amid differences over Washington's rapprochement with Havana.

The Cuban government criticized the meeting between Roberta Jacobson, the State Department's top official for Latin America, and regime critics but indicated that it would not derail negotiations to normalize ties.