Condoleezza Rice, President George W Bush's nominee for secretary of state, has hinted at the direction of future US foreign policy by identifying six "outposts of tyranny" around the world.
US relations with Cuba have been stormy since Fidel Castro took power in 1959, and a US invasion failed in 1961.
Under President Bush, the US has tightened trade and travel regulations still further.
Washington has regularly criticised communist Cuba's rejection of political opposition, and jailing of dissidents.
Two days after Mr Bush's re-election, state department spokesman Richard Boucher said: "The United States condemns the Cuban regime's abuse of
advocates of peaceful change and reform. We call on the regime to cease its repression and release all political prisoners."
President Alexander Lukashenko, in power for a decade, has been accused of crushing dissent, persecuting independent media and political opposition, and rigging elections.
He recently won a disputed referendum allowing him to run for a third term.
Subsequent demonstrations in the capital, Minsk, were violently dispersed.
The US has ties to the opposition and has called for greater democracy.
The Belarus government said Ms Rice's assessment was "quite far from reality".
Foreign Ministry spokesman Andrei Savinykh told the Associated Press news agency: "False stereotypes and prejudices are a poor basis for the formation of effective policy in the sphere of foreign relations."
President Robert Mugabe has been accused of manipulating elections through violence and intimidation, to keep himself in power.
Private newspapers have been forced to close, and white farmers have been forced off their farms so they can be redistributed to black people. Critics claim much of the land has gone to Mr Mugabe's cronies.
The US has imposed targeted sanctions against the president and his associates.
Mr Mugabe says the country's problems - including a collapsed economy and food shortages - are caused by interference from the United States and the UK.
The US accuses Iran of trying to develop nuclear weapons. Iran says it is using nuclear technology just to produce power.
The US and Europe are divided on the best approach to the problem. The US wants the United Nations to consider sanctions, while the EU has been trying to talk Tehran into mutual agreement.
The US also accuses Iran of supporting terrorism.
Ms Rice said Iranians "suffer under a regime that has been completely unwilling to deal with their aspirations and that has an appalling human rights
Known as Myanmar by the military junta that has ruled it for more than four decades, Burma is shunned by many countries in the West.
It is accused by the US of human rights abuses, including the use of slave labour. Thousands of people have been killed in riots against the government.
Democracy activists have been persecuted and jailed. The most celebrated is Nobel Peace laureate Aung San Suu Kyi, who has spent many years under house arrest.
Her National League for Democracy (NLD) won elections in 1990, but was barred from power by the military.
Washington bans trade and aid to Burma, which is also one of the world's largest heroin producers.
The secretive communist state has been accused of human rights abuses on a grand scale, including imprisoning thousands of political opponents and forced labour camps.
No opposition to President Kim Jong-il - son of the dead leader Kim Il-sung - is allowed.
North Korea's isolation has left it with few trade links and a stagnant economy. Hundreds of thousands are thought to have starved to death after famines in the 1990s.
It has also restarted its nuclear weapons programme, leading to a crisis with the outside world and the US. Washington has been trying to push Pyongyang to stop the programme through multi-lateral talks - but North Korea has responded only fitfully.
Ms Rice said: "We must remain united in insisting that Iran and North Korea abandon their nuclear weapons ambitions, and choose instead the path