At least 19 people have been killed and dozens wounded in two car bomb attacks in a town north of Baghdad, police say.
The suicide blasts, in the town of Baiji, targeted the town police chief and a tribal leader, they said.
Al-Qaeda in Iraq has warned it will step up attacks during the Muslim holy month of Ramadan, targeting tribal groups working with US forces.
Meanwhile, Nineveh province deputy police chief Brig Gen Abdul al-Thanon died in a drive-by shooting in Mosul.
In Baghdad, five people were killed and 25 injured when a car bomb exploded in central al-Khulani square at about midday (0900 GMT).
In Baiji, the first bomb exploded at 0600 (0300 GMT) outside police chief Saad al-Nifous' house. Police said he survived the blast.
Minutes later, a second targeted Thamer Ibrahim Atallah, a senior member of the Salahuddin Awakening Council, which is a coalition of tribes fighting al-Qaeda in Iraq.
One report said he had escaped unharmed, but others said his fate was unclear.
Several houses and a mosque were destroyed in the blasts, which were about 1km (half-a-mile) apart.
Last week, a roadside bomb killed a leader of the Salahuddin Awakening Council, Sheikh Muawiya Jebara, and three of his bodyguards near Samarra, about 100km (60 miles) from Baiji in the mostly Sunni Salahuddin province.
The head of the Tikrit-based council, Sheikh Sabah Mutashar al-Shammari, recently said the tribal alliance had conducted more than 100 operations against Sunni militants.
Last month, Sheikh Abdul Sattar Abu Risha - the leader of Anbar Awakening, a similar group in neighbouring Anbar province - was killed in a bomb attack near his home in Ramadi.
US officials have pointed to the formation of the tribal alliances as one of the most positive developments in their efforts to reduce violence in Iraq.
But on Saturday, prominent Sunni cleric Harith al-Dari, who leads the Association of Muslim Scholars in Iraq (AMSI), accused Iraqis fighting alongside US forces of siding with the "occupying enemy", in an interview with Al-Jazeera.
"A decision to stand beside the occupying enemy in order to achieve a wish to stay in Iraq under the pretext of destroying al-Qaeda is neither accepted legally, nor on patriotic or rational grounds," Sheikh Dari said.
Sheikh Dari said AMSI, which groups Iraq's Sunni religious leaders, could talk to al-Qaeda fighters to help them "return to reason", rather than see Iraqis fight with US forces.