Islamic State fighters tightened their siege of the strategic town of Kobani on Syria's border with Turkey on Friday, pushing back Kurdish forces and sending at least two shells into Turkish territory, witnesses said.

Several hundred unarmed protesters who had gathered on the Turkish side of the border in solidarity with the Syrian Kurds broke through a barbed wire fence and rushed towards Kobani in an apparent bid to help defend it.

Islamic State launched its assault on Kobani more than a week ago, besieging it from three sides. More than 140,000 Kurds have fled the town and surrounding villages since last Friday, crossing into Turkey.

U.S.-led air strikes have targeted Islamic State fighters elsewhere in Syria but some Kurdish military officials have said they have made the situation in Kobani more precarious, pushing the Sunni insurgents towards the Turkish border.

Islamic State fighters appeared to have taken control of a hill 10 km (6 miles) west of Kobani from where the YPG, the main Kurdish armed group in northern Syria, had been attacking them in recent days.

The British-based Syrian Observatory for Human Rights, which monitors the war, said Islamic State fighters had also taken control of a village around 7 km to the east of Kobani.

SOUNDS OF SHELLING AND GUNFIRE

The boom of artillery and bursts of machinegun fire echoed across the border, and at least two shells hit a vineyard on the Turkish side, though there were no immediate reports of casualties.

"We're afraid. We're taking the car and leaving today," said vineyard owner Huseyin Turkmen, 60, as small arms fire rang out in the Syrian hills just to the south.

Kurdish forces said on Thursday they had pushed back the advance on Kobani, also known as Ayn al-Arab, but appealed for U.S.-led air strikes on the insurgents' tanks and heavy weapons.

"The clashes are moving between east, west and south of Kobani ... The three sides are active," Idris Nassan, deputy foreign minister in the Kobani canton's Kurdish administration, said by phone from the centre of the town.

"They are trying hard to reach Kobani. There is resistance here by YPG, by Kobani and some volunteers from north Kurdistan -- Turkish Kurds -- who are coming to share in the efforts of Kobani. They have made a strong response," he said.

Kobani sits on a road linking northern and northwestern Syria, and Kurdish control of the town has prevented Islamic State from consolidating its gains. The group tried to take the town in July but was repulsed by local forces backed by Kurdish fighters from Turkey.

"EVERYONE HERE IS ARMED"

"If they did come inside Kobani, everyone here is armed, they are armed and resisting. Even me, I am the deputy foreign minister here in Kobani canton, but I am an armed man too. I am ready to defend Kobani," Nassan told Reuters.

"Every girl, every young man, every man who is able to fight, to carry a gun, they are armed and they are ready to defend and fight."

Turkey has been slow to respond to calls for a coalition to fight Islamic State in Syria, worried in part about links between Syrian Kurds and the Kurdistan Workers' Party (PKK), which has waged a three-decade armed campaign against the Turkish state for greater rights in Turkey's southeast.

The PKK has urged Turkey's Kurds to join the fight to defend Kobani and accused Ankara of supporting Islamic State. Residents in the border area say hundreds of youths have crossed the frontier in defiance of Turkish security forces.

Turkey denies having given any form of support to the Islamist militants, but Western countries say its open borders during Syria's three-year-old civil war have allowed Islamic State and other radical groups to grow in power.

The Turkish military has in the past fired back when shells from Syria's civil war strayed into Turkish territory, and the intensifying battle for Kobani is heightening pressure on Ankara to take a more robust stance against the insurgents.