This is the most serious terrorist violence in Tehran since the turbulent early years after the 1979 Islamic Revolution.

It will come as a huge shock to ordinary Iranians, who have got used to living in a country which is generally far more stable and safer than most of its neighbours.

Iranian intelligence services say a number of people have been arrested, including what they say is a team planning a third attack in the capital this morning.

It’s not clear at this stage who was behind the violence but so-called Islamic State (IS) has claimed responsibility. If confirmed this will be a first.

Despite Iran’s active involvement in fighting IS in both Iraq and Syria the group has so far not carried out any attacks inside Iran, and appears to have little support in this predominantly Shia country.

However in recent months the group has stepped up its Farsi-language propaganda efforts – targeting Iran’s restive Sunni minority, and the Iranian intelligence agencies claim to have foiled an number of IS-inspired plots.