Islamic State (IS) militants have entered the key Syria-Turkey border town of Kobane and taken control of three districts after street-to-street fighting with Syrian Kurd defenders, BBC News reports.

IS fighters entered the eastern districts on Monday, Oct 6, raising their black flag on buildings and hills.

Local officials said about 2,000 civilians fled to the Turkish border.

Taking Kobane, besieged for three weeks, would give IS control of a long stretch of the Syrian-Turkish border. More than 160,000 Syrians, mainly Kurds, have fled the town.

Earlier a local official in Kobane, Idriss Nassan, told the BBC that the town would "certainly fall soon". He confirmed IS was now in control of Mistenur, the strategic hill above the town and that there was heavy shelling. Kobane is now besieged on three sides.

Aircraft from the US-led coalition are reported to have conducted a large air strike in the area at 04:00 (01:00 GMT) on Tuesday, though it is not known what the target was.

Karwan Zebari, a representative of the Kurdish regional government in the U.S., told the BBC it would be catastrophic if IS seized control of the town.

"If this continues, if there's no international aid, military aid arriving for the residents of Kobane and these Kurdish fighters that are fighting in Kobane, it could fall into the hands of IS," he said.

He urged Turkey to take action in support of the residents of Kobane. "I think Turkey's interests, national security, is at stake here as well. It's important that Turkey steps up and assists these Kurdish fighters in repelling this IS momentum."

Mustafa Bali, a spokesman for Kurds in Kobane, told AFP that 2,000 civilians had been evacuated on Monday and that all civilians had been ordered to leave.

The U.S. Central Command earlier confirmed an air strike on Monday by U.S.-led forces had "destroyed two IS fighting positions south of Kobane" but Asya Abdullah, a co-leader of the Kurdish Democratic Union Party representing Syrian Kurds in Kobane, said the strikes in the area were "ineffective".

She said: "[IS has] heavy weapons and tanks, that is why our resistance has limits and we need more air strikes."

Abdullah said: "The rest of the world is silent about this imminent massacre."

Monday saw constant gunfire, with smoke drifting across the rooftops of Kobane and occasional thunderous explosions reverberating across the valley.

A steady stream of Turkish ambulances raced to and from the border, with many wounded people being treated in hospitals close to the frontier.

Turkish Kurds and refugees have clashed with Turkish security forces on the border for the past two days. They are angry at Turkey's perceived inaction over IS in recent months, as well as its refusal to allow them to cross into Syria to fight.

Last week, Turkey pledged to prevent Kobane from falling to the militants and its parliament authorised military operations against militants in Iraq and Syria. But it appears to have taken no action so far.