Jailed Australian filmmaker James Ricketson has taken ill and been moved to the hospital at Prey Sar prison, according to his family and a letter he wrote to the Australian ambassador that was posted to Facebook.

Ricketson, 69, contracted a chest ailment and has been unwell for at least the past three weeks, although he has not been given a diagnosis.

“We’re still unclear about what his exact diagnosis is but he has a persistent chest infection, ongoing skin irritations, loss of energy, loss of weight and frequent dizzy spells,” the Ricketson family said.

The filmmaker was arrested last June for flying a drone above an opposition rally, and was charged days later under Cambodia’s espionage laws with gathering information that could jeopardise national security. If convicted, he could face 10 years in prison.

May 3 marks 11 months since Ricketson was first imprisoned. No trial date has yet been set.

In the letter, Ricketson said he had been taken for an X-ray at Calmette Hospital on April 12 but had not been informed of what it revealed. He claimed a doctor with “no medical training” offered him antibiotics.

His family said they were “deeply concerned” his health would only deteriorate further in the hot season, and called on the Australian and Cambodian governments to move him to a better equipped hospital for a full medical examination and diagnosis.

“Without this we have little faith that his condition will improve,” they said.