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As Turkey announces that it will allow Peshmerga fighters to cross its border into Syria to help defend the town of Kobane from Islamic State militants, the ³ÉÈË¿ìÊÖ's Mark Lowen explains Ankara's relations with the various Kurdish factions and why it is backing Iraqi and not Turkish Kurds in the fight against IS.

"There is no such thing as 'Kurds'. They are simply 'mountain Turks'."

So went the belief of successive Turkish governments in the 1980s and 1990s when the Kurdish insurgency in Turkey was at its height.

Many Kurds were fighting for a separate state; Ankara suppressed the territorial hopes - and greater rights for the Kurdish minority - at any cost.

Over 40,000 people were killed in the armed conflict between the Turkish state and the Kurdistan Workers' Party, the PKK, still outlawed here and labelled a terrorist organisation by Turkey, the EU and the US.

The conflict came to an end in 2012 and a peace process got under way, which endures - just.

That deep-seated hostility towards the PKK has complicated Turkey's relationship with Kurdish fighters in Syria. Their political branch - the PYD - is seen as the PKK's sister party. The Turkish government calls it, and the YPG Kurdish militia, terrorists.

As Ankara blocked Turkish Kurds from crossing into Syria to fight, rage here boiled over and 30 people were killed in Kurdish protests.

But Turkey's stance towards the Kurds in Iraq is very different. As the government of Sunni Turkey fell out with its Shia-led counterpart in Baghdad, the Kurds of northern Iraq were a crucial ally.

And energy became key to the relationship between Ankara and the semi-autonomous Iraqi Kurdistan. Turkey needs the oil produced there, pumping around 120,000 barrels a day through a 600-mile long pipeline from Kirkuk to the southern Turkish port of Ceyhan.

The economic traffic is two-way - Iraq is now the second biggest export market for Turkey, much of it to the Kurdistan regional government. A Turkish company built the new airport at Irbil, the capital of Iraqi Kurdistan.

And so economic advantage has subsumed ethnic division as Turkey's relationship with the Iraqi Kurds blossoms.

That's why Ankara has decided that it's the Kurdish fighters from Iraq who can enter Syria to join the militia, not those from Turkey. Kurds here are still seen through the prism of the PKK, while the Peshmerga in Iraq are part of a semi-autonomous state with which Turkey can do business.

And, trained and armed by the West, the Peshmerga are seen as a far more reliable, and less threatening, ally.

Turkey's government is treading a delicate line - attempting to calm its core nationalist voters at home while bowing to pressure from Washington to help the Kurds in Syria battle Islamic State.

Perhaps, with the Peshmerga move, it has struck a compromise that will help placate all sides.