Iranian security forces have shifted opposition leader Mehdi Karroubi to an unknown location from his Tehran residence where he was being held under house arrest, his website Sahamnews.org said Monday.

Sahamnews.org said the cleric and his wife were shifted from their home late Thursday, and that the transfer was witnessed by a neighbour.

"We have spoken to a neighbour who witnessed our father and mother being taken out of their house," one of the cleric's children, who was unnamed, was quoted as saying by the website.

Eight security vans stopped in front of Karroubi's home at "midnight Thursday" and a "few minutes later they all left with another car," according to the neighbour who said the house had since appeared to be vacant.

Iranian authorities had put Karroubi and fellow opposition leader Mir Hossein Mousavi and their wifes under "complete" house arrest after their supporters staged anti-government protests on February 14, first such demonstration for a year.

The authorities reportedly completely cut off their communication networks as the two leaders had managed to issue statements to their supporters at regular intervals.

The latest statement by Karroubi was through a video posted on his website on February 25 in which he vowed to continue his struggle with "determination".

"I hope that we will overcome the current problems," said the former parliamentary speaker in the video address recorded before his complete isolation.

"We must remain determined on the road of our convictions, and I am certain we will succeed," said the cleric.

"We are committed to the pact we made with the people, to establish the power of the people and Islam based on elections. And on this road, no trouble, no difficulty is too hard to bear," he said.

Karroubi and Mousavi remain steadfast in rejecting the 2009 re-election of President Mahmoud Ahmadinejad who they say returned to power fraudulently.

The protests shook the pillars of the Islamic regime and divided the nation's elite Shia  clergy.