It is a new low for already-chilly relations between Iraq and its neighbour to the north, which have been marred by disputes, including oil exports by the autonomous Kurdish region to Turkey without Baghdad's approval.

"It is not in the interest of Turkey or any other party to underestimate the national sovereignty and violate the rules of international relations and not comply with the most basic regulations in the relations of states and officials," a statement on the foreign ministry's website said.

"All of that was done without the knowledge or approval of the foreign ministry and without going to the official and diplomatic channels to organise this visit," it said.

Davutoglu made his trip to Kirkuk while on a visit to Iraqi Kurdistan, whose leaders have long called for the incorporation of the ethnically divided oil city in their autonomous region in the north, against strong opposition from Baghdad.

Kirkuk province is part of a swathe of disputed territory in northern Iraq that along with oil contracts are the two main points of contention between Baghdad and the Kurdish regional government in Arbil.

The foreign ministry statement termed the visit "blatant interference in Iraq's internal affairs," and said that Turkey should be ready for "the results of this action" and its potential "negative effects on relations between the two countries."

The Kurdistan authorities also came in for criticism in the statement, which said: "We are surprised by the position of the government of the region, which facilitated the visit without the knowledge of the federal government and thereby violated its constitutional responsibilities."

At least 39 people have been killed in violence in the first two days of August, which have seen a number of attacks on security forces and their facilities, including a prison, a military site and checkpoints.

At least nine people were killed and at least 32 wounded in a car bombing in the Husseiniyah area of north Baghdad, medical officials said.

In the northern oil city of Kirkuk, militants attacked the home of a Turkmen family, cutting the throats of a father, mother and two daughters, an AFP correspondent reported.

Gunmen killed seven soldiers and wounded 11 others in three separate attacks south of the city, according to security and medical officials and Shalal Abed Ahmed, mayor of Tuz Khurmatu, where one of the attacks took place.

Gunmen also shot dead four police in Tikrit, north of Baghdad, while three members of the Sahwa anti-Qaeda militia were killed by a bomb near Balad, also north of the capital, security and medical officials said.

And gunmen attacked a checkpoint near a police station northeast of Samarra, killing one police and one Sahwa member, a police captain and a hospital source in Samarra said.

An army officer said that gunmen attacked a checkpoint near Dujail, north of Baghdad, killing a soldier and kidnapping four others.

And Colonel Obeid Ibrahim al-Kataa was killed along with two other police in clashes with gunmen who tried to take control of a checkpoint in Al-Rutba, in the far west, police officers said.

In the Euphrates Valley, a police major said a patrol was hit by a roadside bomb in Haditha, wounding four police, while three police were wounded in another attack by gunmen on a checkpoint east of the town.

South of Kirkuk, six gunmen wearing explosive belts tried to attack a military site but five of them were killed and the sixth seriously wounded and the attack failed, Staff Brigadier General Mohammed Khalaf Saeed al-Dulaimi said.

And a police captain said that three gunmen, one of them wearing an explosive belt, tried to attack a police checkpoint in Baiji, north of Baghdad, but all three were killed.

Al-Qaeda front group the Islamic State of Iraq has said it will look to retake territory in the Muslim holy month of Ramadan in an offensive slammed by Washington as "cowardly", and appealed for Sunni Arab tribes to send fighters in a recording posted in the name of its leader, Abu Bakr al-Baghdadi.

The message posted on various jihadist forums said the ISI would begin targeting judges and prosecutors, and try to help its prisoners break out of jails.

The latest violence comes a day after official figures put the number of people killed in attacks in July at 325, the highest monthly death toll since August 2010.

While violence has decreased compared to its peak in 2006 and 2007, attacks remain common across Iraq. There were attacks on 27 of the 31 days in July.