The IS had threatened to step up its campaign in Iran in recent months

The attackers who stormed Tehran’s Parliament complex and the revolutionary leader’s shrine were Iranian nationals who had joined the Islamic State (IS) group, a top official said.

The six attackers “were Iranian and joined Daesh (IS) from some parts of Iran,” said Reza Seifollahi, Deputy Secretary of Iran’s Supreme National Security Council, on state TV late on Wednesday.

It was the first attack in Iran claimed by the IS, which had threatened to step up its campaign in the country in recent months.

Iran is a key fighting force against the IS and other groups in Iraq and Syria, and the Sunni jihadists consider Iran’s Shia Muslims to be apostates.

Shias make up roughly 90% of Iran’s population, but the country also has a sizeable Sunni minority, particularly around its restive borders with Iraq and Pakistan.