Turkey denied allowing the United States to use its bases against IS, after US officials said access had been granted and that Ankara would also host training for "moderate" Syrian rebels.

American and Saudi warplanes carried out seven new strikes around Kobane, the US military said, including on IS staging posts used in its bid to cut the town off from the outside world.

A Kobane politician who is now a refugee said IS fighters had surrounded Kobane to the south, east and west, and warned of a "massacre" if they take the northern front bordering Turkey.

"If they manage to take control of that area, they will close all access to the town and will begin a massacre," Feyza Abdi said from Turkey.

"That is what they want, to completely enclose the town, cut off all contact with Turkey and engage in barbarism."

Fighting spread to less than a kilometre (half a mile) from the barbed wire frontier fence, with the jihadists carrying out two suicide car bomb attacks in the border zone, said the Syrian Observatory for Human Rights.

With the jihadists advancing on its doorstep, NATO member Turkey has come under intense pressure to take action as part of the US-led coalition that has been carrying out air strikes in both Syria and Iraq.

US officials said Ankara had agreed to let Washington use its bases including Incirlik, in southern Turkey, for the air campaign.

Pentagon chief Chuck Hagel said the agreement included "hosting and conducting training for Syrian opposition members" in Turkey, noting that Ankara would welcome a US Command team next week to "develop a training regimen".

US military planners have repeatedly warned the air campaign alone will not be enough to defeat IS, which in June declared an Islamic "caliphate" in the large parts of Syria and Iraq under its control.

But a Turkish government official told AFP that "there is no new agreement with the United States about Incirlik".

"Negotiations are continuing" based on Turkish conditions previously laid out, the official added.

Turkish Prime Minister Ahmet Davutoglu on Sunday called for military backing for Syria's "moderate opposition" to create a "third force" in the war-torn country to take on the Damascus regime as well as IS militants.

- Iraqis quit Anbar base -

Kobane has become a highly visible symbol of resistance to IS and its fall would give the jihadists control of a long stretch of the Turkey-Syria border.

But concern has also been growing over Iraq, where IS fighters have been threatening to seize more territory.

Iraqi forces are reported to be under intensifying pressure in Anbar province between Baghdad and the Syrian border, where a roadside bomb killed the police chief on Sunday.

On Monday, security sources said Iraqi government troops stationed on the edge of the city of Heet in Anbar had withdrawn to another base, leaving the city under full jihadist control.

Pro-government forces have also been in trouble around Baiji oil refinery south of IS-held Mosul, where US aircraft on Sunday for the first time dropped supplies including food, water and ammunition to Iraqi troops.

Washington has insisted it will not send ground troops back to Iraq, and Secretary of State John Kerry said in Cairo that the Iraqis themselves will have to succeed on the ground.

"Ultimately it is Iraqis who will have to take back Iraq. It is Iraqis in Anbar who will have to fight for Anbar," he said at the weekend.

- Fighters divide up 'slaves' -

IS has committed widespread atrocities in areas under its control, including attacks on civilians, mass executions, beheadings and enslaving women.

In the latest issue of its propaganda magazine Dabiq, IS boasted of having revived slavery, giving Yazidi women and children captured in northern Iraq to its fighters as spoils of war.

IS believes the Yazidis hold deviant religious beliefs and claims that Islamic sharia law allows for their enslavement.

"After capture, the Yazidi women and children were then divided according to the sharia amongst the fighters of the Islamic State," the article said.

The group has also murdered four Western hostages in on-camera beheadings, and on Sunday hundreds of people gathered in northwest England for a memorial service for British aid volunteer Alan Henning.

The 47-year-old taxi driver had travelled to Syria to help Muslim colleagues deliver aid in a convoy, but was kidnapped and his murder claimed by IS in a graphic video released on October 3.

More than 180,000 people have been killed in Syria since an uprising against President Bashar al-Assad's regime began in 2011, evolving into a several-sided civil war that has drawn thousands of jihadists from overseas.

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