The city is at the centre of a tract of disputed territory claimed by both the central government in Baghdad and Kurdish regional authorities in Arbil.

US officials have persistently said the unresolved row is one of the biggest threats to Iraq's future stability.

Senior security leaders quickly insisted in the aftermath of the shootings that they were accidental and did not equate to a conflict between Arab Iraqi forces and their Kurdish counterparts.

"One asayesh (Kurdish internal security) member was killed and five people were wounded, including three Kurdish security members and two policemen, in the clashes," Kirkuk provincial police chief Major General Jamal Taher Bakr told AFP.

"We have arrested four Iraqi soldiers, and we have started an investigation to find out what happened and who is responsible."

Nabeel Shawki, a doctor at Kirkuk city's emergency hospital, confirmed the toll, and added that two of the wounded had been "seriously injured."

Bakr insisted that the shooting was an "accident" and "not a serious incident," and General Samir Abdulkarim, head of the Iraqi army's 12th division in Kirkuk, said it "cannot be considered a conflict between Iraqi army and security forces in Kirkuk."

A police officer in the city, speaking on condition of anonymity, told AFP that an Iraqi army unit had been patrolling an area close to an office of the Kurdistan Democratic Party of Kurdish regional president Massud Barzani.

They were stopped by a plain-clothes asayesh officer, and a shouting match ensued. Guards at the KDP office joined in the argument, and both sides opened fire, leading to the casualties.

Bakr confirmed that an Iraqi army patrol had taken place in the city, where police forces are supposed to take the lead on security matters, but did not give further details.

A US military spokeswoman did not comment when questioned by AFP.

The oil-rich, multi-ethnic and multi-religious province of Kirkuk and its eponymous capital are especially violence prone and are home to Arabs, Kurds and Turkmen.

In an effort to promote cooperation between Arab and Kurdish security forces along the disputed territory of which Kirkuk is at the centre, the US military began conducting tripartite patrols and running joint checkpoints with the two sides at the start of 2010.

Those efforts will conclude when US forces withdraw from the country by the end of this year, according to a bilateral security pact with Iraq.