US President George W Bush has vowed to maintain the trade embargo on Cuba for as long as the government in Havana keeps its "monopoly" on power.
Mr Bush criticised the Cuban regime and encouraged dissidents
Mr Bush said he looked forward to a world without Cuban leader Fidel Castro and urged greater global action to promote democracy in Cuba.
He denounced present-day Cuba as "a tropical gulag".
Cuba rejected Mr Bush's appeal and accused him of promoting violence to bring about a change of regime.
In his first major address on Cuban policy in four years, Mr Bush adopted an uncompromising stance towards the leadership of Cuba.
"As long as the regime maintains its monopoly over the political and economic life of the Cuban people, the United States will keep the embargo in place," he said in a speech at the US State Department.
Mr Bush spoke of citizens there who, he said, had no freedom of employment or expression, who lived in dire circumstances and who feared beatings for pursuing the lives they wanted.
"Now is the time to support the democratic movement growing on the island," he said.
"Now is the time to stand with the Cuban people as they stand up for their liberty. And now is the time for the world to put aside its differences and prepare for Cubans' transitions to a future of freedom and progress and promise."
Mr Bush mentioned the names of dissidents who had been imprisoned for long terms, harassed or persecuted for speaking out against the Cuban communist regime.
He presented dissidents and relatives of dissidents who had escaped Cuba and were present in the audience.
"The dissidents of today will be the nation's leaders," Mr Bush said.
"And when freedom finally comes, they will surely remember who stood with them."
He praised countries like the Czech Republic, Poland and Hungary for the support they were giving to Cuban dissidents and called on other countries to follow suit.
In swift reaction to Mr Bush's speech, Cuban Foreign Minister, Felipe Perez Roque, accused him of promoting the use of force to instigate political change in Cuba.
"It is a confirmation that the current policy of the Bush regime is regime change in Cuba, including through the use of force," Mr Perez Roque told reporters in Havana.
Mr Bush's speech "is understood as a plea for violence, a call for the use of force to topple the revolution and impose his ideas on Cuba," he said.