BAGHDAD — Iraqi officials said Friday they believe that government forces killed Izzat Ibrahim al-Douri, the former deputy of Saddam Hussein who for over a decade was the top fugitive from the ousted regime and became an underground figure involved in Sunni insurgencies, most recently allying with Islamic State militants. Reports of al-Douri’s death came as Iraqi forces are trying to push back Islamic State group fighters in Salahuddin province, where Tikrit is located. No group claimed responsibility for the latest attacks, though the Islamic State has taken credit for similar attacks in the past, especially those targeting Shiites, as well as Iraqi security forces and government buildings. According to the governor of Salahuddin province, Raed al-Jabouri, al-Douri was killed by Iraqi troops and Shiite militiamen in an operation in the Talal Hamreen mountains east of Tikrit, Saddam’s hometown, which was retaken from the Islamic State group earlier this month.