Iraq made a formal protest to Turkey’s envoy in Baghdad yesterday after the Turkish foreign minister made a surprise visit to an oil-rich Iraqi city claimed by both the central government and the country’s autonomous Kurdistan region.

In response, Turkey summoned the Iraqi ambassador in Ankara and warned Baghdad to be “careful” in its remarks.

The latest in a series of diplomatic spats and tit-for-tat summoning of envoys between the neighbouring countries is likely to worsen already strained relations.

Turkish Foreign Minister Ahmet Davutoglu travelled to Kirkuk on Thursday after visiting the regional president in Arbil, the capital of Iraqi Kurdistan.

But Iraq’s foreign ministry accused Turkey of violating its constitution with the visit, saying that Davutoglu had neither asked for nor obtained permission to enter Kirkuk.

A junior minister at Iraq’s foreign ministry handed Turkey’s charge d’affaires a protest letter yesterday, a strongly-worded statement from the foreign ministry said.

“The note also included a demand by the Iraqi government (for an) urgent explanation from the Turkish government,” it added.

Later in the day, the Turkish foreign ministry called in Iraq’s top diplomat in Turkey, an official said.

“The Turkish foreign minister made the visit (to Kirkuk) in a transparent way. There is no secret agenda,” the official from the foreign ministry said on condition his name was not used.

He added that Davutoglu had consulted with Kurdish officials in Arbil before going to Kirkuk in what was called the first visit to the city by a Turkish foreign minister in 75 years.

Relations between Iraq, close to Shia Iran, and Sunni Muslim regional power Turkey were tested after US troops pulled out of Iraq last year and the government immediately tried to arrest one of its Sunni vice presidents.

He fled first to Kurdistan and later to Ankara, where he was given refuge.

Iraqi Prime Minister Nuri al-Maliki and Turkey’s Prime Minister Recep Tayyip Erdogan then traded public insults.

Baghdad’s Arab-led central government and ethnic Kurdish officials are locked in a protracted dispute over who controls territory and oilfields along their internal border. Kirkuk, which possesses huge crude oil reserves, is one of those areas.

Davutoglu yesterday met Iyad Allawi, Maliki’s rival and leader of the Sunni Iraqiya bloc, NTV channel said.

In an interview with NTV, Allawi said the current political crisis could result in Iraq splintering.

“The first course to end the political instability is to share power ... The constitution gives parliament the right to change the government,” Allawi said in comments translated into Turkish on NTV’s website.

“If Maliki does not approach power sharing positively, we will go to parliament for a vote of confidence.”

Iraq and Turkey are also at odds over the worsening conflict in Syria. Turkey has become one of the main backers of the rebels, while Baghdad has refused to support calls for President Bashar al-Assad to step aside.

Iraq is Turkey’s second largest trading partner after Germany with trade reaching $ 12bn last year, more than half of which was with the Kurdish region.

l Shootings and a bombing killed at least six soldiers and five police yesterday, Iraqi security and medical officials said, a day after 33 people were killed in attacks mainly targeting security forces.

At least 50 people, among them 37 members of the security forces, have been killed in violence in the first three days of August, which have seen a number of attacks on soldiers, police and anti-Qaeda militiamen, and their facilities.

A roadside bomb yesterday targeted an army patrol east of Dhuluiyah, killing four soldiers, among them a major, and wounding four others, an army captain and a medical source said.

And gunmen opened fire on a police checkpoint in Baquba, killing four policemen and wounding two more, a police major said.

Gunmen also killed two soldiers and wounded three others in an attack on an army checkpoint near Abu Ghraib, west of Baghdad, an interior ministry official said, while a health ministry official put the toll at six soldiers killed and 15 wounded.

And gunmen with silenced weapons shot dead a policeman and wounded another as they drove in Waziriyah in northern Baghdad, the interior ministry official said.