In some areas of Iraq, Shia militias, trained and funded by Iran, are leading the ground offensive against Islamic State (IS) alongside Kurdish fighters.

American airstrikes have weakened the forces of IS and US Secretary of State John Kerry is confident of building a coalition against it, but has said it would be inappropriate for Iran to join that coalition.

However, the BBC has learnt that Iran already appears to be sending troops and weapons to fight the Sunni extremists.

Gabriel Gatehouse reports from Iraq for BBC Newsnight.