Aides of defeated Iranian reform candidate Mehdi Karroubi called on his supporters to stay away from Muslim prayers to be addressed by supreme leader Ayatollah Ali Khamenei on Friday. Instead Karroubi's campaign office urged supporters to attend an oppositon rally planned for Saturday. Previously Karroubi supporters had been told to turn up for the prayers in Tehran, which are to be broadcast nationwide, wearing black as a sign of mourning for protestors slain in six days of demonstrations over the re-election of President Mahmoud Ahmadinejad last week. But large numbers of hardline supporters of the incumbent, particularly from the Islamic Basij militia, are expected to attend the prayers at which Khamenei is due to make his first public appearance since the protests started. Saturday's rally is being organised by a reformist clerical group, the Association of Religious Combatants. Another of the defeated election candidates, lead challenger Mir Hossein Mousavi, is due to address the rally, which will also be attended by reformist former president Mohammad Khatami, a key Mousavi backer. Official authorisation for the demonstration has been applied for but has yet to be granted. 