Historically, the city accommodates people from Iraq's three biggest ethnic groups: Turkmen, Arabs and Kurds. The groups have been engaged in a prolonged dispute over the city's identity, with each side claiming ownership of the 5000-year-old metropolis.
Being the centre of Iraq's northern oil industry, the Kurds see the Kirkuk region as vital for their long awaited "independent state of Kurdistan". Attacks on the infrastructure of the Kirkuk oil industry have been ongoing since the US-led invasion of Iraq in 2003.
The Kurds' grip on Kirkuk was strengthened after the invasion of Iraq, and the two main Kurdish political parties led by Masoud Barazani, the president of the Kurdistan region, and Jalal Talabani, the Iraqi president, became the main powerbrokers in the city. Now their ambition to annex the city to their intended state has become public and bold.
A referendum is to be held in late 2007 to decide the city's fate. But Arabs and Turkmen say the Kurds are using their political new power and the support of the US to manipulate it.
The situation has provoked Kirkuk's non-Kurdish communities and plunged the city into a fierce war.
"Kirkuk is a small Iraq, where the country's diversity is demonstrated, no party should get hold of it, it is just an Iraqi city"
Attacks on Kurdish targets reached their peak last month when a shrine owned by Talabani's family was attacked on August 27. On the same day, a car bomber blew himself up near the office of Talabani's Patriotic Union of Kurdistan (PUK) in Kirkuk.
Najati Qalaji, secretary-general of the London-based civil rights group the Committee for Defending the Turkmen Rights, expressed serious concerns at the deteriorating situation in Kirkuk.
"Kurds are slowly but surely occupying Kirkuk, everything is for them now, jobs, privileges and power," he said.
Qalaji accused the Kurds of following Saddam's practices.
"Saddam wanted to Arabise Kirkuk and exchanged its Kurdish minority with ethnic Arabs, and the Kurds now are doing the same by scaring people away and bringing in their fellow Kurds in their tens of thousands.
"I do not think there is a need for the referendum because, according to what they are doing now, the result will definitely be 100% in favour of annexing Kirkuk to Kurdistan."
Kurdish parties say the Kurds who have flooded Kirkuk since 2003, many now sleeping rough in public buildings, are those who were thrown out of the city during the Saddam era.
However, the Turkmen say Saddam removed no more than 500 families and that they had ties with the then Kurdish insurgents. Saddam's plan was to prevent them from aiding the insurgency.
"One question I would like to raise here; We know that Kurds who were kicked out by Saddam returned after the invasion and took back their houses by force. So, if those tens of thousands of Kurds who have been sleeping in stadiums and former public buildings were really kicked out of Kirkuk by Saddam, then where are their houses? Why do they not own anything in Kirkuk not even their old identities?" Qalaji said.
Kirkuk's oil industry infrastructure
has been under attack
Non-Kurdish powers in the city reject the Kurdish plan to launch a referendum in late 2007 and say it is just another bid to break Iraq apart and warned they would resist the Kurdish plan.
Leaflets warning inhabitants not to join the army or security forces were distributed in the city last week. The leaflets also urged those serving in the army and security forces to abandon their jobs, or get killed.
Policemen and army officers have suffered countless attacks during the past months.
One Arab activist in Kirkuk, who wanted to be identified as Abu Adnan, said his community is working closely with the Turkmen to prevent the "hijacking of Kirkuk".
"Kurds were never a majority in Kirkuk and the city was never Kurdish, they always shared it with us [Arabs] and our brothers the Turkmen, who always constituted half or two-thirds of the city's population.
"We also should not forget the city's Chaldeans and Assyrians. Kirkuk is a small Iraq, where the country's diversity is demonstrated, no party should get hold of it, it is just an Iraqi city.
"I would like to say that the referendum will be fiercely resisted, we will do everything we can to prevent the hijacking of Kirkuk," he said.
Joost Hiltermann, director of Crisis Group's Middle East Project, said: "For the Kurds, this deadline could be a self-laid trap. Having raised expectations, Kurdish leaders must now deliver by the end of 2007 or meet public wrath [among Kurds]".
The group issued a report last month urging an international action to prevent Kirkuk from turning into a scene of savage civil war.
In 1959, Kurdish communists took advantage of the support of Abd al-Karim Qassim, then Iraq's ruler, and massacred Kirkuk's Turkmen elite.
Sami Abd al-Hamid, an Iraqi communist leader, said the massacre has been wrongly blamed on the communists.
"It is true that those who performed the killing were communist Kurds, but they acted as Kurds not as communists, they were absolutely ethnic Kurds killing their rival Turkmen," he said.
In 1991, Kurdish rebels seized Kirkuk after the Iraqi army's chaotic withdrawal from Kuwait, which caused a short power vacuum in Iraq.
Kurdish gunmen launched an organised killing campaign against Kirkuk's Arab and Turkmen inhabitants. Iraqi Republican Guards regained the city from Kurdish rebels shortly afterwards.