Mira says the House of Saudi is unreformable

"The regime is unreformable," said Saad al-Faqih, from the UK-based Movement for Islamic Reform in Arabia (Mira).

The protests will take place peacefully on Thursday after noon prayers in Riyadh and Jeddah, Mr Faqih said.

Public dissent is outlawed in Saudi Arabia, ruled since its foundation in 1932 by an absolute monarchy.

In October 2003 Saudi police broke up another protest organised by Mira, detaining dozens of demonstrators.

Reports last October said a heavy police presence prevented any serious demonstrations from materialising when the group last called for protests.

Elections looming

The exiled group has broadcast several messages on its website and television channel encouraging Saudi citizens to join the protests.

"The ruling family not only rejects reforms, but is not capable [of them]," it said in one statement.

"The regime has lost its legitimacy and the conditions are ripe to start a global action aimed at changing the regime."

In another broadcast monitored by the BBC, Mr Faqih said that demonstrators are ready for possible harsh treatment by the security forces and some "have written their wills".

The protest call comes as Saudi Arabia is preparing for landmark municipal elections which will be held next year in three rounds.

The first popular vote in Saudi history is part of a reform package launched by the ruling House of Saud in response to international and domestic calls for political and social change.