Fidel Castro has appeared on Cuban television for the first time since June 2008 and his photograph was published in an official newspaper yesterday in a signal that his health has improved.

The 83-year-old met with a group of Venezuelan students in a three-hour meeting that took place on Saturday.

He told them he was worried about the future of the planet, under threat from global warming.

‘Even the Pentagon has gotten involved,’ Mr Castro said.

‘It has included the climate among things that threaten the security of the United States.’

‘We are facing events that are very, very, very grave,’ the former leader said.

He resigned the presidency last year and was replaced by his brother Raul Castro, 78.

Fidel Castro had not been seen in public since July 2006, when he underwent intestinal surgery for a still-undisclosed ailment.

His health is considered a state secret.

The video followed a front-page photograph of Mr Castro meeting with Ecuadorean president Rafael Correa, published yesterday in the newspaper Juventud Rebelde.