Two days of heavy air strikes by US warplanes have slowed an advance by Islamic State militants against Kurdish forces defending the Syrian border town of Kobani.

Last week Turkish and US officials said Islamic State were on the verge of taking Kobani from its heavily outgunned Kurdish defenders, after seizing strategic points deep inside the town.

The tempo of coalition air strikes has increased dramatically, with US fighter and bomber planes carrying out 14 raids against Islamic State targets near Kobani on Wednesday and yesterday, the US military’s Central Command said.

The strikes had seen the militants’ advance slow, but “the security situation on the ground in Kobani remains tenuous,” the US statement added.

The four-week Islamic State assault has been seen as a test of US President Barack Obama’s air strike strategy, and Kurdish leaders say the town cannot survive without arms and ammunition reaching the defenders, something neighbouring Turkey has so far refused to allow.

Islamic State has been keen to take the town to consolidate its position in northern Syria after seizing large amounts of territory in that country and in Iraq. A defeat in Kobani would be a major setback for the Islamists and a boost for Obama.

Smoke rises from the Syrian town of Kobani yesterday. Photo: Reuters

Heavy and light weapons fire were audible from across the border in Turkey yesterday, with one stray mortar hitting Turkish soil close to abandoned tents, a Reuters correspondent said.

Turkish security forces moved civilians and media away from hills overlooking Kobani as the fighting raged.

Six air strikes hit eastern Kobani and there was fierce fighting between Kurdish and Islamist fighters overnight on Wednesday, but neither side made significant gains, according to the British-based Syrian Observatory for Human Rights. Kurdish fighters later managed to seize a street in Kobani that had been held by militants, the Observatory said. A journalist in Kobani said air strikes had allowed Kurdish forces to go on the offensive for the first time since Islamic State launched their assault four weeks ago.

“We walked past some (YPG) positions in the east yesterday that were held by IS only two days ago,” Abdulrahman Gok told Reuters by telephone.

“Officials here say the air strikes are sufficient but ground action is needed to wipe out IS. YPG is perfectly capable of doing that but more weapons are needed.”