(CNN) - Democratic presidential candidate Barack Obama said Tuesday the resignation of Cuban President Fidel Castro should "mark the end of a dark era in Cuba's history."
In a written statement, the senator from Illinois added:
"Fidel Castro's stepping down is an essential first step, but it is sadly insufficient in bringing freedom to Cuba. Cuba's future should be determined by the Cuban people and not by an anti-democratic successor regime.
"The prompt release of all prisoners of conscience wrongly jailed for standing up for the basic freedoms too long denied to the Cuban people would mark an important break with the past. It's time for these heroes to be released.
"If the Cuban leadership begins opening Cuba to meaningful democratic change, the United States must be prepared to begin taking steps to normalize relations and to ease the embargo of the last five decades. The freedom of the Cuban people is a cause that should bring the Americans together."
John McCain, R-Ariz., also issued a written reaction to the media.
"Today's resignation of Fidel Castro is nearly half a century overdue. For decades, Castro oversaw an apparatus of repression that denied liberty to the people who suffered under his dictatorship.
"Yet freedom for the Cuban people is not yet at hand, and the Castro brothers clearly intend to maintain their grip on power. That is why we must press the Cuban regime to release all political prisoners unconditionally, to legalize all political parties, labor unions and free media, and to schedule internationally monitored elections.
"Cuba's transition to democracy is inevitable; it is a matter of when - not if. With the resignation of Fidel Castro, the Cuban people have an opportunity to move forward and continue pushing for the moment that they will truly be free. America can and should help hasten the sparking of freedom in Cuba. The Cuban people have waited long enough."
Democrat Hillary Clinton also welcomed the news that Castro is stepping down.
She told an economic roundtable: I just want to say a word about a development today that is very significant. Fidel Castro has decided to step down as the leader of Cuba.
"And I think this provides a great opportunity for the people of Cuba. I am hoping that the new leadership will take steps to move Cuba toward democracy - release political prisoners - lift a lot of the oppresive burdens that have prevented the Cuban people from really having the kind of future they deserve to have.
"Certainly the people of the United States would meet a new government to talk about what needs to happen if that new government takes some action that demonstrates they are willing to change. So, we are hoping that we see some evidence of that.
"It is a very stark reminder that even if you have been in power for 50 years - you cannot hold onto power forever, and the people of Cuba deserve to have leadership that respects their human rights and gives them the opportunity to you know fulfill their own destiny.
"And we need a president who will work with countries around the world in Europe and the Western Hemisphere to push Cuba now to join the community of nations and to become a democracy. And I will certainly do that as president."
Former Arkansas governor and Republican presidential candidate Mike Huckabee said in a statement that "The Cuban people deserve nothing less than free and fair elections which would provide the only hope for a prosperous and democratic Cuba.
"Until Fidel Castro is dead, there can be no significant movement towards reform in Cuba. Raul Castro has proven that he's as much a tyrant and dictator as his brother Fidel. Simply providing more power to another dictator does nothing to promote freedom and democracy to the Cuban people."
Update (12:20pm) to include Clinton and Huckabee statements
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