The sudden departure of Iran’s leading nuclear and security official was greeted with dismay in Tehran political circles amid concern that a power struggle at the highest levels of the regime has exploded into the open.

In western capitals too, the announcement that Ali Larijani, head of the Supreme National Security Council, had resigned, to be replaced by a deputy foreign minister close to President Mahmoud Ahmadi-Nejad, raised fresh worries about Iran’s nuclear policy.