There are still several hurdles for Barack Obama and Raul Castro to clear. Photo: Reuters

In a speech, President Raul Castro also called for the lifting of the US trade embargo and Cuba's removal from a terror list.

Last month the two countries announced a thaw in relations, agreeing to restore diplomatic ties. They were severed in 1961.

High-level talks were held last week.

A Congressional delegation arrived in Havana to begin negotiations aimed at reopening embassies in the two countries' capitals.

Meanwhile, former Cuban leader Fidel Castro appeared to signal his approval for the political rapprochement.

Cuba's state-run newspaper published a letter on Tuesday in which he wrote: "We will always defend co-operation and friendship with all the people of the world, including with our political adversaries."

He wrote that although he did not "trust the policy of the US", it did not mean he rejected a "peaceful solution to conflicts".

'Illegally occupied'

His brother Raul, who succeeded him as president in 2008, made his demands at the summit of Community of Latin American and Caribbean States in Costa Rica.

"The reestablishment of diplomatic relations is the start of a process of normalising bilateral relations," he said. "But this will not be possible while the blockade still exists, while they don't give back the territory illegally occupied by the Guantanamo naval base."

The land on which the base stands was leased to the US government in 1903 by Cuba's then-rulers.

US officials have so far not responded to Mr Castro's remarks.

President Barack Obama has called on Congress to put an end to the trade embargo, which has been in place since 1962.

Earlier this month he also used his executive powers to loosen trade and restrictions on travel to the Caribbean island.