-Venezuelan doctor Jose Rafael Marquina said the 86-year-old was in a vegetative state and is 'moribund' at a house in western Havana
-He also claims that Venezuelan President Hugo Chavez had travelled suddenly to Havana to be with his friend and ally
-A letter from Castro has been published by state media denying he was on death's door and relatives have also denied the claims
-Castro has not been seen in public since he met Pope Benedict XVI in March
The revolutionary Cuban leader Fidel Castro has suffered a massive stroke and has only weeks to live, a doctor has claimed.
Jose Rafael Marquina said the 86-year-old was in a vegetative state and is 'moribund' at a house in western Havana.
Despite this, a letter from Castro was published by state media denying he was on death's door. Relatives have also denied the claims.
Marquina told Spain's ABC newspaper that Castro had suffered a 'massive embolism of the right cerebral artery' and while not on life support or breathing artificially, was 'moribund' at a house in a gated former country club in the Cuban capital.
Marquina also said that Venezuelan President Hugo Chavez had travelled suddenly to Havana to be with his friend and ally.
Support: The doctor also claimed that Venezuelan President Hugo Chavez, right, had travelled suddenly to Havana to be with Castro, left
Reached by The Associated Press, Marquina said his sources were in Venezuela, but he would not identify them or say how they were in a position to have information about Castro's health.
He also indicated he had received corroborating evidence from sources on Twitter, but would not say who.
His claims have been reported on social media sites and by some news organisations. However, Marquina, has made some claims before that have not panned out.
In April, Marquina said that Chavez, who has been battling an undisclosed kind of cancer, was in his 'last days' and would not last to November. With less than two weeks to go, the Venezuelan leader says he's beaten the illness and appears stronger in public.
Castro's health is considered a matter of national security in Cuba and few details are released.
Rumors that the former Cuban leader has died or is near death have circulated repeatedly for years, but they gained force after he failed to issue a public statement congratulating Chavez on his October 7 election victory.
Castro has not been seen in public since March, when he received visiting Pope Benedict XVI. He has also stopped writing his once-constant opinion pieces, the last of which appeared in June.
There was no immediate comment from the Cuban government on the latest claims, but a letter attributed to Castro was published Thursday by Cuban state media. In it, he congratulated graduates of a medical school on the occasion of its 50th anniversary.
Two close family members of Castro have also recently denied he is in grave condition. Juanita Castro, the former leader's sister, told the AP in Miami that reports of her brother's condition are 'pure rumors' and 'absurd'.
Son Alex Castro told a reporter for a weekly Cuban newspaper that his father 'is well, going about his daily life'.