One bomber detonated an explosives-rigged vehicle at the southern entrance to Tikrit, while the other blew up an ambulance in Samarra, the officials said.
Jassem al-Jbara, the head of Salaheddin province's security committee, said the Tikrit attack killed 12 people and wounded 20, while six people died and 12 more were hurt in Samarra.
Security and medical officials confirmed the attacks, but gave higher tolls.
IS issued a statement claiming the attacks, but said there were three suicide bombers: two who struck Samarra and the third hitting Tikrit.
Iraqi forces are fighting to retake Mosul, the jihadist group's last major urban stronghold in the country, in a massive operation that was launched on October 17.
IS has carried out a series of diversionary attacks since the start of the Mosul offensive in a bid to draw both attention and forces away from the battle.
But aside from the names of the two bombers, the IS statement made no reference to Mosul.
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