* Kurds fear Islamic State attack on Syrian city

* IS fighters have swept over villages in northern Syria

* 45,000 refugees have crossed into Turkey - deputy PM (Adds Kurdish official, context)

By Seyhmus Cakan

SANLIURFA, Turkey, Sept 20 (Reuters) - Tens of thousands of Syrian Kurds have crossed into Turkey over the past day, fleeing an advance by Islamic State fighters who have seized dozens of villages close to the border, Turkish Deputy Prime Minister Numan Kurtulmus said on Saturday.

Turkey opened a stretch of the frontier on Friday after Kurdish civilians fled their homes, fearing an imminent attack on the Syrian border town of Ayn al-Arab, known as Kobani in Kurdish.

"Around 45,000 Syrian Kurds have crossed the border as of now from eight entrance points along a 30-km distance from Akcakale to Mursitpinar since we opened the border yesterday," Kurtulmus told CNN Turk television.

Islamic State's advances in northern Syria have prompted calls for help by the region's Kurds who fear an impending massacre in the town of Kobani, which sits in a strategic position on the border.

Esmat al-Sheikh, head of Kurdish forces defending Kobani, said clashes were taking place north and east of the town on Saturday.

Islamic State fighters using rockets, artillery, tanks and armoured vehicles had advanced further towards Kobani overnight and were now within 15 km (9 miles) of the town, he told Reuters by telephone.

At least 18 Islamic State fighters were killed in clashes with Syrian Kurds overnight as the militant group took control of more villages around the town, according to the Syrian Observatory for Human Rights, which monitors the war.

Iraqi Kurdish leader Masoud Barzani called on Friday for international intervention to protect Kobani from the Islamic State advance, saying the insurgents must be "hit and destroyed wherever they are".

The United States is drawing up plans for military action in Syria against the radical Sunni Muslim group which has seized swathes of territory in Syria and Iraq, proclaiming a caliphate in the heart of the Middle East.

Western states have increased contact with the main Syrian Kurdish political party, the PYD, whose armed wing is the YPG, since Islamic State led a lightning advance in Iraq in June.

The YPG says it has 50,000 fighters and should be a natural partner in a coalition the United States is trying to assemble to fight Islamic State.

But such cooperation could prove difficult because of Syrian Kurds' ties to the Kurdistan Workers' Party (PKK), a group listed as a terrorist organisation by many Western states due to the militant campaign it has waged for Kurdish rights in Turkey. (Additional reporting by Asli Kandemir in Istanbul and Sylvia Westall in Beirut,; Writing by Nick Tattersall; Editing by Janet Lawrence)

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