Analysis
By Daniel Schweimler BBC correspondent in Havana

Nothing is ever simple in relations between the United States and Cuba.

As former US President Jimmy Carter packed his bags for his visit to Havana, hopes were being raised in both countries that it might herald a new period of greater understanding.

Mr Carter is the highest profile US politician to visit cuba since Fidel Castro took power

Mr Carter will after all be the highest profile US politician to visit Cuba since President Fidel Castro came to power 43 years ago.

He was invited by the Cuban leader and arrives with the permission of the US authorities, who normally impose a travel ban to the communist-led island on most other American citizens.

Positive signs

His visit also comes after US companies last November began selling food to the country for the first time since Washington imposed a trade embargo on President Castro's government 40 years ago.

The signs, on one level at least, looked positive.

Then the US Under Secretary of State, John Bolton, accused Cuba of having the capacity to develop biological weapons and transferring its technical expertise to countries hostile to Washington.

He firmly identified President Castro's government as part of America's 'axis of evil', highlighting the fact that the Cuban leader last year visited several US foes, including Libya, Iran and Syria.

The timing of the accusation surprised some in Washington.

However, it will have pleased the fiercely anti-Castro Cuban exile community in Miami which might have felt that the Carter visit was showing Cuban/US relations in too positive a light.

John Bolton identified Cuba as part of America's 'axis of evil'

Cuba, it could be argued, had done much to ensure that Mr Carter's trip would be fruitful.

Human rights

A week before the visit, the authorities released the country's highest profile political dissident, Vladimiro Roca, from prison.

Cuba is sensitive about criticism of its human rights record.

There is no legal opposition on the island although the authorities do tolerate a small, fragmented dissident movement, accusing its members of being counter-revolutionaries in the pay of the government's enemies in the United States.

Mr Carter is expected to meet with some of them. Cuba is also sensitive to accusations that it is soft on terrorism.

It was quick to offer its condolences to the American people after 11 September but equally quick to criticise the way the US conducted the war in Afghanistan, highlighting in the state-run media the deaths of innocent civilians.

Relations between the governments in Havana and Washington are possibly as bad now as they have been at any time since President Castro came to power in 1959.

Life after Fidel

But that is on the government level. President Castro has always made it plain that his argument is not with the American people, and has in the past few months gone out of his way to welcome sympathetic US politicians, actors and above all business people to Havana.

The official line is that Raul Castro will takeover from Fidel

The US mostly seems content to wait until life after Fidel, whenever that may be. But it is in the meantime jockeying to be in the best possible position to take advantage of the chaos many feel his demise will bring.

The official Cuban line is that Fidel's younger brother, Raul, will take over and the revolution, which is about more than just one man, will live on.

Few Cubans dare to question that premise openly. But many independent analysts feel that without Fidel the house will come tumbling down.

But he has defied the critics and the odds so many times over the past 43 years that only a fool would predict with any certainty what will happen to Cuba and to Cuban/American relations A.F - after Fidel.

Jimmy Carter may be the best placed person for many years to at least cast a little light on the situation.