Iraq's political and ethnic rivalries have long converged on Kirkuk, the northern city that commands the country's biggest oilfields.
Kurds claim Kirkuk as their own
The Kurds of northern Iraq see it as a potential seat of power, a site of emotional as well as economic significance.
Meanwhile real power, until recently, has rested with the city's Arab population, boosted by migrants from the south under Saddam Hussein's "Arabisation" programme.
Located 250km (155 miles) north of Baghdad at the foot of the Zargos mountains, Kirkuk lies next to the Kurdish autonomous area of northern Iraq.
It is the country's fourth-largest city and has a population of about 700,000. It is built by the Hasa river on an area with archaeological remains more than 5,000 years old.
The oldest part of the town is clustered around a citadel built on an ancient mound.
Its capture and that of the surrounding oil fields was one of the main objectives in the US invasion of Iraq. After the fall of Saddam Hussein's regime, Kurdish guerrilla forces briefly occupied the city.
Their fighters swept into the city, before being withdrawn amid fears of unsettling the Iraqi Arabs and ethnic minorities such as the Turkmen.
Turkey too, with its own restive Kurdish community, considered Kurdish control of the Iraqi oilfields - and their capability to form an independent state - to threaten Turkish interests.
Since the fall of Saddam, thousands of Kurds forced out of the region have begun returning - and thousands of others still dream of doing so.
The fate of the Kurdish fighters and refugees has become central to the horsetrading between the Shia Arab and Kurdish politicians who performed best in Iraq's elections and are now trying to govern together.
While the Kurds want Kirkuk to accommodate some 100,000 refugees, the Arabs want the Kurdish guerrilla force to be disbanded.
The Kurdish bloc's ultimate aim is for Kirkuk to be attached to the three provinces which are recognised by Baghdad as the autonomous area of Iraqi Kurdistan.
The interim Iraqi constitution adopted in 2004 (the Transitional Administrative Law or TAL) specifies a process to reverse the consequences of the previous regime's polices and to hold a referendum to determine the wishes of Kirkuk's people.
As part of coalition negotiations, the Kurdish bloc have demanded written commitments and timetables for action on Kirkuk.
But as Kurdish politician Barham Saleh warned in 2004, getting Kirkuk wrong would be "a recipe for civil war".
At stake are the surrounding oilfields, said to account for half of Iraq's total oil output, and the legitimacy of the new Iraqi government.
British explorers tapped open the region's oil reserves in the early 20th Century, paving the way for decades of exploitation by international companies.
Pipelines connect Kirkuk's oilfields to ports on Turkey's Mediterranean coast.
Vulnerable to sabotage, they were blown up in clashes between the Kurds and Saddam Hussein's army and later, by insurgents opposed to the US presence.