Airstrikes have reportedly targeted Islamic State positions in northern Syria close to the besieged Kurdish town of Kobane, amid claims that the attacking warplanes approached from Turkey.

Residents reported a number of aerial raids overnight around Kobane, a strategic point which has been under assault from IS fighters for days, forcing thousands of residents to flee towards Syria's neighbour a few miles to the north.

The raids have not been confirmed by the United States or any of the partners in an international coalition which began airstrikes inside Syria on Tuesday.

But civilians in the area reported that the strikes took place around midnight and that the jets involved came from the direction of Turkey, according to a UK-based monitoring group, the Syrian Observatory for Human Rights.

Witnesses said that the strikes hit supply roads used by the Islamic State around 20 miles outside Kobane, the group said, adding that "civilians from the area said that the warplanes came from the Turkish lands."

Meanwhile IS fighters clashed with forces of the YPG — Syrian Kurdish defense units — around six miles to the south west of the town, the Observatory reported.

Ismit Sheikh Hassan, the YPG chief of defense in Kobane, told VICE News from the town that there had been a number of strikes overnight in the area but that he could not confirm the exact locations.

He reported that IS fighters had advanced around one mile overnight and on Wednesday morning and were now as close as four miles from the town.

Hassan said new fighters were coming to join the YPG from Turkey and elsewhere, but that with no supplies of ammunition or arms coming in, they were at a disadvantage against the heavy weapons of the Islamic State.

"Until now they [airstrikes] didn't have a positive effect, but if they attack ISIS positions it might make a difference," the YPG commander said.

"If they [the coalition] attack ISIS it would be very useful. If not, we will defend our city to the end."

Another YPG fighter on the Western front reported that he had heard jets overhead but didn't know where the strikes took place.

He told VICE News the airstrikes were helping but said the sheer numbers of IS fighters made it difficult to hold off their assault on the city. "There's too many, if you kill 200, 400 take their place," the fighter said.

Turkey has denied that it carried out any strikes or that its airspace or bases, including the US airbase at Incirlik, had been used.

The Turkish daily Hurriyet noted, however, that just ahead of the strikes President Recep Tayyip Erdogan had said he was considering military involvement in the fight against IS.

He told reporters on the sidelines of a United Nations meeting in New York that Turkey was now looking at a role that "includes everything. Both military and political" — a move that would represent a shift in stance for a country that has so far been reluctant to get openly involved in the conflict.

"Of course we will do our part," Erdogan said.

Turkish authorities are struggling to cope with the influx of Syrian refugees, with around 130,000 reported to have arrived at the border in recent days. Security forces have clashed with Kurds coming from inside Turkey to protest in solidarity with the refugees, as well as to try and cross into Syria to join the fight against IS.

A group of refugees waiting at a border crossing to get back into Syria were in a defiant mood on Wednesday, chanting "Kobane! Kobane!" Mostly men, who said they had left their families in Turkey, but some of them women and children, the refugees said they were going to fight IS and to support the YPG with logistics and supplies.

One man, who did not give his name, was confident IS could still be prevented from taking Kobane. "We can still save it, is still strong," he told VICE News, adding that airstrikes would be beneficial. "It would be very helpful if they attacked IS, IS are cowards and when they see jets, they run away."

Kurdish activists have warned that Kobane could become "a second Shingal" if the IS advance is not halted, referring to the Yazidis of Shingal in northern Iraq, tens of thousands of whom were stranded on Mount Sinjar without food or water after fleeing IS in August.

A international coalition led by the US and involving several Gulf state partners began strikes inside Syria on Tuesday in the first direct foreign military involvement in the country since the start of the conflict.

Up to 200 strikes have been carried out in neighbouring Iraq in an attempt to halt the advance of the group which has taken control of swathes of territory in the two countries in its bid to establish an Islamic caliphate.

The US-led coalition reported two more airstrikes in Syria overnight, bringing the number of raids conducted so far to 16.