An Irish citizen, being held in a prison in Iran, should be released as quickly as possible, Ireland's Tánaiste (deputy prime minister) has said.

Micheál Martin added that he was "very concerned" for Bernard Phelan, who is originally from County Tipperary and also holds French citizenship.

He was arrested on 3 October during a wave of anti-government protests in Iran.

The 64-year-old went on hunger and water strike on New Year's Day but suspended the protest earlier this week.

Mr Martin said the Irish government has been "very clear" with Iranian authorities that Mr Phelan should be released.

Mr Phelan, who was travelling on a French passport, was arrested for allegedly taking photographs of police officers and a mosque which had been burned.

He has denied multiple charges including disseminating anti-regime propaganda and taking pictures of security services.

Conditions inside Vakilabad Prison in Iran's second largest city Mashhad are said to be cramped, with 16 people sharing a cell amid freezing night-time temperatures.

Speaking to RTÉ Radio 1's This Week programme, external, Mr Martin said he had spoken to the Iranian ambassador last week and was seeking further engagement.

Mr Phelan has a heart condition and a chronic bone issue but Iranian authorities have refused to release him on medical grounds.

Previously, French government officials said they were "extremely worried about his health, which is poor and requires appropriate medical monitoring, which is not ensured in detention".

Mr Martin said: "We are very concerned, we share the concerns of his family and we have made very strong representations to the Iranian authorities for his release on humanitarian grounds."