Jihadists are waging fierce street battles with Kurdish militia backed by US-led air strikes in a Syrian border town whose fall would mark a major victory for the Islamic State group.

With the fight for Kobane entering a crucial phase, the IS jihadists fought to extend their foothold on Tuesday into new areas in the south and west of the town, a day after piercing its Kurdish defences.

Gunfire was heard from the other side of the Turkish border, while a Kurdish flag was seen flying in the centre of Kobane, also known as Ain al-Arab.

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Fresh US-led air strikes targeted IS positions in the southwest of the town.

Kobane is seen as a strategic prize whose capture would give IS a long stretch of the border with Turkey for its self-proclaimed “Islamic caliphate”, which already spans large parts of Syria and Iraq.

The IS jihadists “are trying hard to capture the city”, Idris Nahsen, a Kurdish official still in Kobane, said by telephone.

Turkish tanks sit in wait near the town of Kobane. Photo: Getty

He said they were meeting resistance from the Kurdish People’s Protection Units.

The Kurds have repeatedly called for increased foreign military support to stop Kobane falling to IS, an extremist Sunni Muslim group.

“We need help from the international community,” Nahsen said. “Either we finish them (IS) or they will finish us.”

At least 34 IS jihadists and 16 Kurdish fighters were killed in fighting in Kobane on Monday, according to the Syrian Observatory for Human Rights.

IS fighters have seized a number of buildings in the south and west of Kobane, including a hospital under construction, according to the Britain-based monitoring group.

Kurdish fighters have ordered civilians to evacuate the town, after the jihadists planted their black flags on its eastern side and entered Kobane on Monday.

The Kurdish fighters are optimistic that their knowledge of the town’s layout will compensate for their light weapons, said local activist Mustafa Ebdi.

“They are fighting to defend their town and they say they will fight to the last person,” he said.

Ebdi said the latest US air raids had little effect.

“The strikes hit the Mishtenur area,” he said, referring to a plateau south of Kobane.

“But they (IS) aren’t gathered there. There are other places they should be hitting,” he said.

In a sign of mounting desperation, a Kurdish female fighter blew herself up at an IS position east of Kobane on Sunday, the Observatory said.

It was the first reported instance of a female Kurdish fighter employing a tactic often used by the jihadists, said the monitor, which relies on a network of sources inside war-ravaged Syria for its reports.

IS jihadists began advancing on Kobane three weeks ago, quickly capturing a string of villages surrounding the town and prompting about 186,000 residents to flee across the Turkish border.

An official in the Turkish town of Suruc said on Tuesday that 700 people, including 47 wounded, had crossed the border from Syria overnight, both civilians and Kurdish combatants.

Seven dead bodies were also carried across the frontier.

Turkey last week won parliamentary approval for military intervention against IS in Syria and Iraq, but it has yet to announce any plans for military action despite the advance of the jihadists to its doorstep.

On Monday, officials said the US military has started flying attack helicopters against the jihadists in Iraq for the first time, marking an escalation in the air war that puts American troops at higher risk.

In all, nearly 2000 air raids have been launched by the coalition in both Iraq and Syria, US defence officials said.

– AAP