Tehran (AFP) - Iran's ex-president Mohammad Khatami on Sunday asked supreme leader Ayatollah Ali Khamenei to intervene in the case of two reformist politicians under house arrest without trial for the past six years.

The two high-profile reformists -- Mehdi Karroubi and Mir Hossein Mousavi -- have been under house arrest since 2011 for their part in mass protests that rocked the regime two years earlier.

"I want to request the supreme leader to intervene to ensure that the house arrest is resolved," said Khatami, who led a reformist government between 1997 and 2005, and is himself banned from appearing in the media since the protests.

"The responsible institutions cannot or do not want to resolve the issue of the house arrests and only your intervention can allow this issue to be resolved, which is in the interests of the regime and would be a sign of its strength," he said, addressing Khamenei.

The issue has returned to the fore after Karroubi, 79, went on a brief hunger strike Wednesday to demand a trial.

He gave up the strike the following day after reportedly gaining assurances from the government that they would at least remove intelligence agents who had recently been posted inside his home.

But on Sunday, the spokesman for the judiciary denied that the agents had been removed, saying this was "lies", according to local media.

Karroubi and Mousavi were candidates in the controversial 2009 presidential election, and accused the regime of massively rigging the result in favour of hardliner Mahmoud Ahmadinejad.

They played a key role in the ensuing months of protests -- nicknamed the Green Movement -- with Karroubi earning particular ire from the regime for claiming that protesters were being raped and tortured in jail.

Khamenei and hardliners refer to the Green Movement as "the sedition", and he has repeatedly called on the leaders to repent before there can be any talk of their release.

The fate of Mousavi and Karroubi played a significant role in the re-election of moderate President Hassan Rouhani this May, with reformist voters chanting their names at his rallies.

There is concern that Karroubi's death could act as a lightning rod for renewed protests.

He has been hospitalised several times in the past month, undergoing surgery for a weak heart.