Iran today faces the prospect of a bloody Sunday after opposition supporters clashed violently with security forces yesterday at the start of a key religious ceremony that had been identified beforehand as a dangerous flashpoint.

The Observer has learned that the authorities have cancelled all leave for police and emergency services over the two days in anticipation of violence, while hospitals have been put on full alert to expect multiple casualties. The order is effective until midnight tonight.

“Cancelling leave means we are in for a very violent time,” a paramedic said. “The authorities are very scared. They are prepared for everything and anything.”

Mehdi Khalaji, an Iranian analyst at the Washington Institute for Near East Policy, warned that Khamenei would resort to ever more brutal methods to preserve his leadership. “Mohammad Khatami [Iran's reformist former president] was asked during a visit to Washington last year why he hadn’t done more to resist Khamenei,” he said. “He replied that it was because Khamenei is determined to fight his enemies if they come to the streets and that he is ready to kill up to 200,000 people. There are many pieces of evidence that confirm Khatami’s understanding that Khamenei is prepared to kill more people.