The AP is reporting that:
Backed by allied Shiite and Sunni fighters, Iraqi security forces on Monday began a large-scale military operation to recapture Saddam Hussein's hometown from the Islamic State extremist group, state TV said, a major step in a campaign to reclaim a large swath of territory in northern Iraq controlled by the militants.
This operation will, if successful, set up the Iraqi army for the much bigger fight to retake Mosul, an operation that is vastly more challenging and unlikely to proceed this spring as some had been predicting.
Al-Iraqiya television said that the forces were attacking Tikrit from different directions, backed by artillery and airstrikes by Iraqi fighter jets. It said the militants were dislodged from some areas outside the city, but gave no details.