The Najaf attack, which involved gunmen and a suicide car bomb, followed blasts a day earlier in Baghdad that left 29 people dead, a reminder of Islamic State's continued ability to operate away from territory under its control.
The recapture of Mosul would probably spell the end for the group's self-styled caliphate in the areas it seized in 2014, but the militants would still be capable of fighting a guerrilla-style insurgency in Iraq, and plotting or inspiring attacks on the West.
Since the U.S.-backed offensive began on Oct. 17, elite forces have retaken a quarter of Mosul in the biggest ground operation in Iraq since the 2003 US-led invasion that toppled Saddam Hussein. Prime Minister Haider al-Abadi has said the group would be driven out of the country by April.