Tikrit battle a 'learning experience'
Iraqi forces and Shia militias are on the offensive in Tikrit, taking on Islamic State forces in Saddam Hussein's hometown.
It's the biggest push yet against the militants who have overrun large parts of the country. A victory would be both strategically and symbolically important.
Retired Lieutenant General James Dubik, now a Senior Fellow at the Institute for the Study of War, once headed the training of Iraqi forces. He says the battle for the key town will be testing for the forces on the offensive.
"I think there will be a lot of learning on their part. The Tikrit battle will be very very difficult," he said.
Dubik joined the BBC's Laura Trevelyan to discuss the battle and US efforts against Islamic State.