Ankara (AFP) - Far from sharing Western euphoria over Kurds' capture of a key border town from Islamic State (IS) jihadists, Turkey is alarmed by the advance of Kurdish forces, fearing that they could create a powerful autonomous region on its doorstep.

Backed by US-led airstrikes, fighters with the Kurdish People's Protection Units (YPG) militia this week seized the key Syrian border town of Tal Abyad from IS jihadists.

There was jubilation over the victory among Kurds, who hailed the end of the notoriously repressive practices in Tal Abyad by IS, which has captured swaths of Iraq and Syria.

But while Turkey insists it is no friend of IS, Ankara's reactions to the Kurdish advance have ranged from the circumspect to the outright hostile.

President Recep Tayyip Erdogan said he was troubled by the advance of Kurdish forces, fearing they could in the future create a structure to threaten Turkey.

"This is not a good sign," he said. "Everyone needs to take into account our sensitivities on this issue."

Deputy Prime Minister Bulent Arinc accused Kurdish forces of implementing an "ethnic cleansing" campaign against non-Kurdish Arab and Turkmen populations.

He said they were trying to link together the three Kurdish-led cantons of northern Syria -- Jazira, Kobane and Afrin -- into a single autonomous Kurdish region known to Syrian Kurds as Rojava.

But in a thinly veiled attack on Turkey, the YPG lashed out at "unfounded slander" it said was being propagated by sides annoyed by the defeat of IS.

"We repeat openly that as the YPG, we will ensure Syrian unity and not the dissolution of Syria," it said in a statement.

- 'We won't allow' -

Turkey's relations over the last years have warmed with the autonomous region of Iraqi Kurdistan in northern Iraq. But the last thing it wants to see is the appearance of a similar region on its 911-kilometre (566-mile) border with Syria.

Turkey accuses the YPG -- the military wing of the main Kurdish party in Syria, the Democratic Union Party (PYD) -- of being the Syrian offshoot of the Kurdistan Workers' Party (PKK) which has waged a bloody three-decade insurgency in its southeast.

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With Kurds making up 20 percent of Turkey's population, its ultimate nightmare would be Turkish Kurds cooperating with Syrian Kurds in search of autonomy on both sides.

A Turkish official, speaking on condition of anonymity, said the PYD had not cut its links with the PKK and was leading a "systematic and planned" campaign to change the demographic composition of Tal Abyad.

"Not only the Arabs and Turkmens but also Kurdish factions not linked with PYD are being expelled from there," the official told AFP.

Turkey has taken in some 23,000 refugees since the fighting for Tal Abyad began early this month but says they are mainly Arab and Turkmen Syrians, not Kurds.

"A serious policy is under way to leave the region under PYD domination," the official said. "We will not allow that."

- 'Turkey shouldn't worry' -

Alarms bells were first set off in Ankara in 2012 when Syrian President Bashar al-Assad withdrew his forces from majority Kurdish areas in the north and entrusted the security there to Kurdish militia.

Ankara later tried to open dialogue channels with the PYD. Its leader Salih Muslim visited Turkey several times as Turkish authorities pushed Syrian Kurdish groups to join forces with rebels fighting Assad.

On Wednesday, Muslim assured Turkey that YPG and other armed forces would pull out from Tal Abyad once order was restored, to be followed by the formation of a civilian administration representing all parties.

"Turkey should not worry. The two sides of the border are our people. How can we be hostile to our own people?... Turkey should get rid of its fears," he told the Hurriyet daily.

NATO-member Turkey, a vocal critic of Assad, has refused to play a greater role in a US-led coalition against IS radicals, and instead called for a broader strategy with the ultimate goal of bringing down Assad's Damascus regime.

Nihat Ali Ozcan, analyst from Ankara-based think tank TEPAV, said the Kurds were now being able to avenge the Syrian regime's policy of Arabisation in the 1960s.

"The story that began with IS is shading into ethnic clashes threatening to spill over into Turkey," he told AFP.