Islamic State fighters are pushing towards a key Kurdish town on Syria's border with Turkey, whose parliament is set on Thursday to consider authorising military intervention against the jihadists on its doorstep.

Kurdish fighters backed by US-led air strikes were locked in fierce fighting Wednesday to prevent the besieged border town of Ain al-Arab from falling to the Islamic State group fighters.

"There are real fears that the IS may be able to advance into the town... very soon," the Syrian Observatory for Human Rights warned, with the jihadists within three kilometres (two miles) of the strategic town.

The fighting came as 41 children and seven adults were reported dead in twin bombings at a school in the government-controlled central city of Homs, which has been devastated by the three-year civil war.

There was no immediate claim of responsibility.

NATO member Turkey, after months of caution, has decided to harden its policy, with parliament due to debate Thursday a government request to authorise military action against IS in both Iraq and Syria.

Ankara has not yet indicated what form its assistance could take although Erdogan has repeatedly called for a buffer zone on the Turkish border inside Syria -- backed by a no-fly zone -- to ensure security.

According to the Hurriyet daily, quoting sources in Turkey's central command, the request seeks permission from parliament for the presence and transit of foreign soldiers in Turkish territory and deployment of Turkish military forces to Iraq or Syria.

Ankara has previously justified its low-key role in the fight against IS by saying its hands were tied by concerns over the fate of dozens of Turkish hostages abducted by IS in Iraq.

But those hostages were freed September 20, prompting what Erdogan has acknowledged as a major change in Turkish policy.

- 'Bodies thrown in the air' -

Anti-jihadist air strikes and the heavy clashes in and around Ain al-Arab killed at least 18 people Wednesday -- nine militants and nine Kurdish fighters, the Syrian rights observatory said.

"Kurdish fighters on the front lines saw the bodies literally being thrown into the air" by the force of the blast, the observatory's human rights director Abdel Rahman said.

Abdel Rahman said the vastly outgunned Kurdish fighters were forced by the jihadists' advance to retreat from the fight on the western outskirts, in order to defend the edges of the town itself.

Ain al-Arab would be a major prize for IS, giving it unbroken control of a long stretch of the Syrian-Turkish border.

The twin blasts in Homs farther south hit a neighbourhood inhabited mainly by the Alawite community of Syrian President Bashar al-Assad, which has been frequently targeted by rebels and jihadists.

The Pentagon has warned there will be no quick and easy end to the fighting, with spokesman Rear Admiral John Kirby saying: "No one should be lulled into a false sense of security by accurate air strikes."

Turkish President Recep Tayyip Erdogan echoed that dropping "tons of bombs" on IS would provide only temporary respite.

- 16 killed in Baghdad car bombing -

About 191,000 people have been killed since an uprising against Assad erupted in 2011, escalating into a several-sided war involving pro-government forces, hardline jihadists and more moderate rebels.

The US-led coalition of Western and Arab allies has been flying missions in Syria since last week against IS, an extremist Sunni group that has seized control of large parts of the country and neighbouring Iraq.

A coalition warplane killed nine militants in a strike on an IS base near Hawijah, a senior Iraqi intelligence officer said.

In Baghdad, a suicide car bombing ripped through a busy commercial street, killing at least 14 people, police and medical sources said.

Iraqi Foreign Minister Ibrahim al-Jaafari said any international assistance in the fight against IS should preserve "Iraqi sovereignty," and also thanked Iran for its support.

"Iran has provided assistance to Iraq, as have some other countries. This is not a secret and we have to thank them for it," he said.

- Australia joins air campaign -

Australia announced that its jets were joining the air campaign in Iraq in a support capacity.

Prime Minister Tony Abbott, who has called IS an "apocalyptic death cult," said the aircraft would provide reconnaissance and refuelling support.

Britain said its jets targeted two IS vehicles west of Baghdad overnight in their second strikes on the jihadists in Iraq in as many days.

France, which currently has six Rafale warplanes and just under 1,000 soldiers based in the United Arab Emirates, said it would deploy three more Rafales and a warship in the coalition fight against IS in Iraq.