The largest delegation from the US Congress to visit Cuba since the 1959 revolution has arrived in Havana.
Raul Castro has indicated he may consider improving ties with the US
The 10 members of the bipartisan group favour the easing of US sanctions on Cuba and are seeking dialogue.
Jeff Flake, a Republican congressman heading the delegation, said he hoped to meet officials and launch a "new era in US-Cuba relations".
It is not clear whether the team will meet acting President Raul Castro, who has called for better ties with the US.
President Fidel Castro, 80, temporarily ceded power to his brother after having emergency intestinal surgery in July.
The US broke official ties with Cuba following Fidel Castro's rise to power in 1959 and has had an economic embargo in place against the island since 1960.
The US delegation will spend three days in Cuba, during which time members are due to meet several high-ranking Cuban officials.
Made up of six Democrats and four Republicans, the party is led by Mr Flake, a Republican from Arizona, and William Delahunt, a Democrat from Massachusetts.
President Fidel Castro last appeared on television in October
The BBC's Americas editor Emilio San Pedro says the timing of the visit, coming as Cuba undergoes what could be described as its most significant internal political transformation in decades, is important.
However it remains unclear whether the trip will be anything more than symbolic, our correspondent says.
The visit has been criticised by some opponents of the Castro regime in the US, including Cuban exiles in Miami, who say that economic interests should not be put before human rights in Cuba.
The Bush administration has also shown no signs of embracing a thaw as long as Cuba's communist system remains intact and political prisoners remain in jail, our correspondent adds.
Acting leader Raul Castro has given several indications that he may be open to a warming of relations.
A fortnight ago, he used an address at a military parade held to mark his older brother's 80th birthday to attack the US - but also to renew an offer to hold talks with Washington.
Fidel Castro did not appear at the parade and has not been seen in public since 26 July.
His last appearance on Cuban TV, looking frail and wearing pyjamas rather than his trademark military fatigues, was in late October.
The top US intelligence official, John Negroponte, has told the Washington Post newspaper that the president is believed to be very ill and close to death.
"Everything we see indicates that it will not be much longer... months, not years," he told the Post.