KEY POINTS:
A new war is threatening Iraq just as the world believes the country is returning to peace.
While violence is dropping in Baghdad and in the south of the country, Arabs and Kurds in the north are beginning to battle over territories in an arc of land stretching from Syria to the Iranian border.
A renewal of the historic conflict between Arabs and Kurds in Iraq, which raged through most of the second half of the 20th century, would seriously destabilise the country as it begins to recover from the United States occupation and the Sunni-Shiite civil war of 2005-07.
The crisis between the Government of the Iraqi Prime Minister, Nouri Maliki, and the Kurds, who make up 20 per cent of the population, is coming to a head now because a resurgent Iraqi Army is beginning to contest control of areas which Kurds captured when Saddam Hussein fell in 2003.
There has been a mounting number of clashes between predominantly Arab Iraqi Army units and the Kurdish peshmerga forces along a 420km line that stretches diagonally across the northern third of Iraq, from Sinjar to Khanaqin in the south.
The tensions underpinning the conflict have always attracted less international attention than the US-Iraqi war or the Shiite-Sunni conflict.
Yet if the conflict develops into a full-scale war it will complicate President Barack Obama's plan to withdraw 142,000 US soldiers from Iraq over 16 months and redeploy many of them to the US military effort in Afghanistan.
In some respects, the Arab-Kurdish war has already started. Kurdish leaders say that in Nineveh province, Sunni Arab gunmen have killed 2000 Kurds and 127,000 Kurds have turned into refugees during the past six years.
Baghdad and Basra have become safer in the past year but Mosul, the capital of Nineveh and Iraq's third largest city, remains one of the country's most violent places.
Khasro Goran, the Kurdish Deputy Governor of Nineveh province, who operates from heavily-fortified headquarters in Mosul, said it was "not acceptable" for non-Kurdish military units to move into disputed areas. "If they try to do so, we will stop them."
On the streets outside Goran's office, once a Baath party office and now the headquarters of the Kurdistan Democratic Party, an array of competing military forces holds power.
His immediate guards are tough-looking Kurdish peshmerga in uniform. As we left their compound, they fired a shot to deter a driver who got too close.
Two hundred metres further on, we passed a small Iraqi Arab unit covering a crossroads with a light machine gun mounted on a cream-coloured Chevrolet pick-up truck.
Close by, a policeman held an AK-47 assault rifle. He was part of a mostly Sunni Arab force recruited in Nineveh which changed sides during an insurgent offensive in 2004 and joined the anti-government guerrillas. The rebels captured 31 police stations.
Mosul is majority Sunni Arab but, on the east bank of the Tigris river, there are large Kurdish districts that are overlooked by a mosque on a small hill, where the Prophet Jonah is reputedly buried.
Most of the Kurds living west of the Tigris have fled or have been killed. The Christian community was driven out by attacks last year, although some Christians are now returning.
There have been so many bomb attacks in Mosul that, in many places, damage is no longer repaired.
The city is al Qaeda's last stronghold in Iraq. Earlier this month, a bomb killed four US soldiers and an interpreter while gunmen killed two prominent local politicians.
On Monday, US and Iraqi government forces said they had launched a campaign to eradicate al Qaeda in the province, although US troops were being used only for back-up.
The Kurds in the oil province of Kirkuk and in Diyala province have also often been targeted by suicide bombers. For their part, Arabs in these areas accuse the Kurds of launching a campaign of ethnic cleansing.
The Kurdish regional Prime Minister, Nechervan Barzani, says that if the disputes are not settled by the time the Americans withdraw, "it will be war between both sides".
What makes the situation so explosive in Nineveh and across the north is that, during the past year, the balance of power has been changing in favour of the Arabs and against the Kurds.
Minority Kurds had dominated the provincial government in Nineveh and Mosul after Sunni Arabs, despite being in the majority, boycotted the local elections four years ago. But polls last month reversed the balance, sweeping an Arab Iraqi party, Al Habda, to dominance in the provincial council.
The Iraqi Army is also becoming stronger. It contains Kurdish and Arab units but it is the non-Kurdish units that are being sent north.
MOSUL - FORCED MARRIAGE
* Iraqi Kurds, who speak their own language and have their own identity, did not want to be part of Iraq when its borders were drawn after the collapse of the Ottoman Empire in World War I.
* They often rebelled in pursuit of independence or autonomy and suffered terribly under Saddam Hussein.
* During the Kuwait war, they rose up but were defeated.
* They created an autonomous zone outside Baghdad's control and since the United States invasion have had autonomy through the Kurdistan Regional Government, but they control a much larger area where Kurds are the majority - this is the area now disputed.
* The Kurds are also an essential part of Iraq's coalition Government.
- INDEPENDENT
