Germany’s top human rights official has urged Iranian authorities to release opposition leaders MirHosein Mousavi and Mehdi Karroubi.

Markus Leoning, the German Commissioner of Human Rights, said Thursday that these two individuals “are being held at an unknown location and completely cut off from the outside world without any legal justification” and he called for their immediate release, Associated Press reports.

Mousavi and Karroubi, who ran against Mahmoud Ahmadinejad in the 2009 presidential election, challenged the result of that election and accused the government of vote fraud. The allegations triggered widespread mass protests, which authorities violently crushed.

Last February, the two opposition leaders rallied their supporters to take to the streets in solidarity with the Arab uprisings in the region. They were quickly put under house arrest and have been completely cut of from the outside world.

The demonstrations they had organized for February 14 were also crushed by security forces and remain the last mass street protest put up by the opposition.

The opposition says that Mousavi and Karroubi are imprisoned together with their wives, but the authorities deny this and maintain that they are merely banned from issuing announcements.

Over the past five months, the opposition leaders have only been allowed limited visits with immediate family members under heavy security.

Most recently, MirHosein Mousavi’s mother-in-law, Navvab Safavi, reported that on her last visit with the couple, she found them both very pale and noticeably thinner.

Iran’s Islamic Society of Physicians has urged the authorities to allow independent doctors to examine the opposition leaders. The government’s refusal has intensified concerns over the opposition leaders’ well-being.