It is called the "trigger line", a 300-mile long swathe of disputed territory in northern Iraq where Arab and Kurdish soldiers confront each other, and which risks turning into a battlefield. As the world has focused on the US troop withdrawal from Iraq, and the intensifying war in Afghanistan, Arabs and Kurds in Iraq have been getting closer to an all out war over control of the oil-rich lands stretching from the borders of Syria in the west to Iran in the east.
The risk of armed conflict is acute because the zone in dispute is a mosaic of well-armed communities backed by regular forces. Kurdish and Arab soldiers here watch each other's movements with deepest suspicion in case the other side might attempt to establish new facts on the ground. It is to avert a new armed conflict breaking out between the powerful military forces on both sides that Iraq's Prime Minister, Nouri al-Maliki, travelled to Kurdistan for crisis talks last week with Kurdish leaders, Iraq's (Kurdish) President, Jalal Talabani, and the President of the autonomous Kurdistan Regional Government (KRG), Massoud Barzani. Mr Maliki and Mr Barzani had not met for a year during which their exchanges have been barbed and aggressive.
The 26th Brigade of the 7th Division of the Iraqi army, an Arab unit, recently tried to move from Diyala province northeast of Baghdad through Makhmur, where there is a Kurdish majority, to reach the mainly Sunni Arab city of Mosul. Fearful this might be a Baghdad government land-grab for Makhmour, Kurdish civilians blocked the road. Khasro Goran, a senior member of the ruling Kurdistan Democratic Party (KDP), says the army advance would have been resisted if it had gone on. "Our forces had taken up positions on higher ground and if the Iraqi army brigade had come on, they were under orders to open fire." Ominously for the future unity of Iraq, the Kurdish unit preparing to shoot was itself part of the Iraqi army.
American mediation and Arab-Kurdish negotiations in Baghdad ultimately prevented a clash and the 26th Brigade withdrew without fighting. But according to Mohammed Ihsan, the KRG's Minister for Extra Regional Affairs, who has responsibility for the disputed territories, any outbreak of hostilities could be the start of a major conflict: "If fighting does start at one point I am sure it will quickly spread along the whole line from Sinjar [near Syria] to Khanaqin [near Iran]."
President Barack Obama's administration is alarmed by the prospect of Iraq splitting apart just as the US pulls its troops out. But Washington can also see the danger of becoming more deeply enmeshed in the Arab-Kurdish conflict, which kept northern Iraq ablaze for much of the last century. US withdrawal also frightens the Kurds, the one Iraqi community that supported the US-led invasion. They can see the political and military balance is swinging against them just as they are faced by Mr Maliki's rejuvenated Iraqi government commanding the increasingly confident 600,000-strong Iraqi security forces. A report by the International Crisis Group concluded recently that "without the glue that US troops have provided, Iraq's political actors are otherwise likely to fight all along the trigger line following a withdrawal, emboldened by a sense that they can prevail, if necessary, with outside help."
Arab leaders, both Shia and Sunni, claim that the Kurds have overplayed their hand since 2003. As Saddam Hussein's regime was disintegrating, Kurdish forces swept into the cities of Mosul and Kirkuk, seizing territories where there was or had been a Kurdish majority before Saddam Hussein's ethnic cleansing. The sole sign of one of the 3,500 Kurdish villages destroyed by Saddam is often a pathetic pile of stones in a field where people once lived before they were killed or forced to flee, their herds of cows and flocks of sheep slaughtered, and concrete poured down the village well.
Kurdish vociferousness over the danger of renewed war with the Arabs stems partly from wanting to panic the US into staying involved in the dispute. Yet the danger of war is quite real as the Kurds genuinely fear being evicted from the disputed territories and driven back into the KRG, behind the Green Line established after the Kurdish uprising of 1991.
The Kurds nervously watch Iraqi troops reoccupy positions once held by Saddam Hussein's army. Last year, the Iraqi army sent north its 12th Division, a 9,500-strong force that is at least 75 per cent Shia Arab, into the Kirkuk oil province. "These troops are trying to encircle Kirkuk just as Saddam used to do," says Safeen Dizayee, the spokesman for the KDP. "They are trying to push out our forces, both peshmerga [Kurdish fighters] and Kurdish units in the regular Iraqi army."
Anti-Kurdish feeling is running high in the rest of Iraq, as is fear of Iraqi Arab revanchism in Kurdistan. Ethnic and sectarian hatred is strongest in the disputed territories where different communities live side-by-side. Nineveh province is like an Iraqi Lebanon in its diversity with its complicated mix of Kurds, Kurdish speaking Yazidis, Shabak, Sunni Arabs, Shia and Sunni Turkomans as well as Chaldean and Assyrian Christians.
Asked about the prospect of an Arab-Kurdish civil war, people from Mosul say that for them it started six years ago. Some 2,000 Kurds from the city have been killed and another 100,000 have fled. Until January this year, the minority Kurds ruled the local council because the Sunni Arabs boycotted the election of 2005. But in the latest election, the anti-Kurdish al-Hadba party won and their leader, Atheel al-Najafi, is the new provincial governor, though this does not mean he can enter Kurdish areas. When he tried, on 8 May, to enter Bashiqa, a Yazidi-Chaldean town on the main road from Mosul to Arbil, at the head of a convoy of 40 police cars Kurdish peshmerga said they would shot to kill if he tried to go on.
Moderation is not in fashion along the "trigger line". One Iraqi army battalion commander has been dismissed and investigated for cowardice over a confrontation with Kurdish security in January. It took place at Altun-Kupri, a Kurdish-Turkoman town which occupies an important position on the road between Arbil and Kirkuk. An Iraqi army patrol had suddenly appeared in town and local Kurds and Kurdish police immediately took to the streets to protest. Violence was only averted because the battalion commander, now sacked for his moderation, ignored orders from his high command to open fire.
In the disputed areas, people say they will fight for dilapidated villages and infertile stretches of semi-desert which hardly seem worth dying for. But the land here is more valuable than it looks. One of the reasons for sensitivity about the exact position of the border separating Arabs from Kurds is that the disputed territories lie on top of Iraq's northern oil and gas fields centred on Kirkuk. The forays by the Iraqi army towards Makhmur and Altun Kupri had extra significance for the Kurds because both towns are so close to these oilfields.
Kurds and Arabs in Iraq have the strength to thwart each other. The KRG has awarded contracts for oil development to foreign companies which have found oil, but the oil can only be exported using Baghdad government oil pipelines. "Otherwise, they will have to carry it away in buckets," says the Iraqi Oil Minister, Hussein al-Shahristani. The Kurds counter that at least one vital Iraqi oil pumping station is on their territory.
War between Arabs and Kurds in Iraq would doom the country as an independent state. Such a conflict is not winnable by either side and each would seek foreign allies. For all their brutality, Saddam Hussein and his predecessors failed to crush the Kurds over 40 years. Differences over Kirkuk, the disputed territories and control of oil run too deep to resolve quickly, but after his long-delayed meeting with Kurdish leaders, Mr Maliki needs at least to stop a further escalation of the Arab-Kurdish conflict.
Rebellious history: The Iraqi Kurds
*The Iraqi Kurds began revolting in 1919 after the British had seized what was to become modern Iraq. The British wanted to include Kurdistan in Iraq to create a defensible military line for the new country.
*From 1960-1975, the Kurds rebelled under the leadership of Mullah Barzani. Saddam Hussein defeated them in 1975 when he convinced the shah of Iran to abandon his support for the the Iraqi Kurds.
*Resistance resumed in 1980 when Saddam Hussein invaded Iran. In the al-Anfal punishment campaign in 1988, the Iraqi Army massacred 180,000 Kurds and destroyed 3,500 out of 4,000 villages.
*Days after Iraq's defeat in Kuwait in 1991, the Kurds, under Massoud Barzani of the Kurdistan Democratic Party and Jalal Talabani of the Patriotic Union of Kurdistan, recaptured most of Kurdistan. An Iraqi counter-attack led to US protection.
*The Kurds established an autonomous enclave but fought a civil war. Supported by the US in 2003, they captured Kirkuk and Mosul and areas where there is or was a Kurdish majority before ethnic cleansing.