An opposition website says Iran's main opposition leader who has been under house arrest since 2011 was briefly taken to hospital for medical tests.

It's reportedly the third time that Mir Hossein Mousavi was taken to a heart hospital in the past two years.

The report by Kaleme.com says doctors recommended Mousavi remain in the Tehran hospital where he was brought late on Tuesday but his guards refused to let him stay. There were no details on his condition.

The 71-year-old Mousavi ran against President Mahmoud Ahmadinejad in the 2009 election. Reformers claimed Ahmadinejad's victory was fraudulent and demonstrations rocked Iran for weeks, after which authorities moved to crush the opposition.

Mousavi and fellow opposition leader Mahdi Karroubi were effectively silenced and placed under house arrest in early 2011.