Iranian opposition leader Mehdi Karroubi, under house arrest for six years, ended his hunger strike late Thursday after the government agreed to remove intelligence agents from his home.

However, his demand to face trial -- he has never been charged since being placed under house arrest in 2011 -- appears no closer to being granted.

Karroubi, 79, stopped eating and drinking on Wednesday morning and was hospitalised a day later with high blood pressure.

His son, Mohammad Hossein, told the reformist Jamaran website that Karroubi had met with Health Minister Hassan Ghazizadeh Hashemi on Thursday, and secured promises that convinced him to end the hunger strike.

Sahamnews, a website linked to the Karroubi family, said the government had promised to remove the agents from his home.

Karroubi and fellow reformist leader Mir Hossein Mousavi were candidates in Iran's disputed 2009 presidential election which sparked months of mass protests over claims that the polls were rigged in favour of hardline incumbent Mahmoud Ahmadinejad.

Both were placed under house arrest in 2011 for their role in the protests, which were brutally put down by the regime. 

Former president Mohammad Khatami, the figurehead of the reformist movement who has been banned from appearing in the media since the protests, said there was nothing he could do to secure a trial.

"The fact that I cannot do anything to remove these worries makes me even more sad," he told Karroubi's son, according to Sahamnews.

Karroubi's wife Fatemeh told Sahamnews earlier this week that his first demand was the removal of intelligence ministry agents and security cameras that had been recently installed inside their home, which she said "has no precedent before or after the (1979 Islamic) revolution in any house arrest".

"Second... in case of continuation of the house arrest, they should arrange a public trial," she said.

Karroubi "does not expect a fair trial" but wants it to be public and would respect the verdict, she added. 

In March, his son Mohammad Hossein was sentenced to six months in prison for "propaganda against the regime" after he published a letter that his father had written to Iran's current president, Hassan Rouhani, calling for a trial.

Karroubi's failing health -- he underwent a heart operation earlier this month -- poses a potential problem for the Iranian regime, with fears that it could provide a lightning rod for renewed protests.

He remained in hospital on Friday as doctors monitored his condition. 

Rouhani, considered a political moderate, won a resounding re-election victory in May, in part by rallying reformists and vowing to win the release of Mousavi and Karroubi.

But hardline judiciary chief Ayatollah Sadegh Larijani threw cold water over Rouhani's promises shortly after the election.

"Who are you to end the house arrest?" Larijani said in May.