US-led forces have carried out at least five air strikes against the Islamic State of Iraq and the Levant (ISIL) outside Kobane, a monitoring group has said, after the group's fighters pushed to within 2km of the Syrian-Kurdish town.

The strikes on Wednesday hit ISIL fronts south and southeast of the town, also known as Ain al-Arab , which the group has been battling to take for more than two weeks, the UK-based Syrian Observatory for Human Rights said.

ISIL had continued closing in on the town near the Turkish border, despite multiple US air strikes on Tuesday, as the US defence department said it could not "bomb the militants into obscurity".

"No one should be lulled into a false sense of security by accurate air strikes," the department's spokesman, John Kirby, said. "We will not, we cannot bomb them into obscurity."

The US and UK also bombed ISIL positions in Iraq as Kurdish peshmerga forces launched a ground assault on Tuesday.

A long-term effort will be needed to train and arm Syrian rebel forces and strengthen Iraq's army, he said.

Tuesday's advance was the closest ISIL had come to Kobane since it began an advance nearly two weeks ago, sending tens of thousands of mostly Kurdish refugees fleeing across the border.

NATO member Turkey, after months of caution in the fight against ISIL, has decided to harden its policy, and the government asked parliament on Tuesday to authorise military action against them in Iraq and Syria.

Politicians are due to debate a motion on Thursday that deputy prime minister Bulent Arinc said would "meet all the demands and eliminate the risks and threats".

Turkey has remained silent about what its intervention would entail, but Arinc indicated the parliamentary mandate would be kept as broad as possible to allow the government freedom to decide.

In a separate development, three car bombs killed at least 13 people and wounded 41 in Shia-dominated areas of the Iraqi capital Baghdad on Tuesday, police and hospital sources said.