Apparent revenge attacks after clashes between protesters and Iraqi security forces entered a second day on Wednesday, killing 12 people, while three more died in other unrest, officials said.
The violence brings the toll since Tuesday to 84 dead, 66 of them in clashes and attacks involving security forces, protesters and their supporters.
The unrest is the deadliest so far linked to demonstrations in Sunni areas that erupted more than four months ago.
Protesters have called for the resignation of Shiite Prime Minister Nuri al-Maliki and railed against the alleged targeting of their community by the authorities.
In the deadliest incident on Wednesday, gunmen killed five soldiers and wounded five more in the Sulaiman Bek area north of Baghdad, a high-ranking army officer and an administrative official said.
Iraqi MP Ashwaq al-Jaf issued a statement saying that dozens of people were wounded in air attacks by the Iraqi military in the area, and the army officer confirmed that helicopters were used in the fighting.
In other violence that officers said was apparently in revenge for clashes on Tuesday, gunmen attacked a Sahwa anti-Al-Qaeda militia checkpoint in Khales northeast of Baghdad, killing four militiamen and wounding a fifth, a police lieutenant colonel and a doctor said.
Gunmen also wounded a policeman in the northern city of Mosul, while a soldier was wounded in another shooting to its south, police and a doctor said. Three gunmen were also killed in the Mosul attack.
Apparently unrelated violence in Tarmiyah, north of Baghdad, and Fallujah, west of the capital, killed three more people and wounded at least 10, officials said.
The trouble began early on Tuesday when clashes broke out after security forces moved into an area near Hawijah in north Iraq, where protests have been held since January.
The initial fighting killed 27 people, while a series of revenge attacks left another 27 dead on Tuesday, and 15 more were killed in apparently-unrelated unrest.
Two Sunni ministers quit in the wake of the initial violence, bringing the number of Sunni cabinet members who have resigned since March 1 to four.
On Wednesday, mourners buried dozens of people killed the day before.
Hundreds of mourners walked on the main road past the provincial council building in Kirkuk city alongside vehicles carrying 34 coffins, an AFP journalist said.
They chanted "We sacrifice for you, Iraq" and "We will take revenge for the martyrs of Hawijah," continuing on to Hawijah, to the west of the city, where the dead were buried.
"What happened was a massacre, and the situation is catastrophic and dangerous, and we should work on easing the tension," said deputy Kirkuk governor Rakan Said.
A protest organiser and a doctor also said on Wednesday that two Iraqi soldiers who were kidnapped by demonstrators the day before near Ramadi, west of Baghdad, have been released.
Protest organiser Abdulrazzaq al-Shammari said the soldiers were handed over to a hospital in the city, and the doctor said one of them who was wounded was still in hospital, while the other was released.
Shammari also said that the demonstrators were demanding that soldiers withdraw from all cities in Anbar province, where Ramadi is located, and stay in their main bases.