Preparations are under way in Iran for mass rallies to mark 31 years since the Islamic revolution.

The opposition wants its supporters to join in, but the country's police chief has said any unofficial slogans will not be tolerated.

In an interview to Al Jazeera, Ali Motahari, one of the country's most prominent conservatives, but also one of the few politicians to openly criticise the government's role in the current political crisis, says everyone, including the opposition, should be allowed to take to the streets.