Jihadists are on the verge of seizing the key Syrian border town of Kobane, Turkey warned Tuesday, after a three-week assault by the Islamic State group that has killed hundreds.

The fall of Kobane to IS would be a major victory for the jihadists, who are fighting for a long stretch of the border with Turkey for their self-proclaimed "Islamic caliphate".

With the battle entering a crucial phase, US and Arab warplanes launched fresh strikes on IS positions near Syria's third largest Kurdish town.

AFP correspondents on the Turkish side of the border reported hearing at least eight air strikes on and around Kobane during the day, with most of the strikes concentrated in the morning and late afternoon.

Black smoke was seen rising from several points in the town and one air strike resulted in a fire that was clearly visible from the Turkish side.

A Pentagon statement issued in the middle of the day confirmed five coalition strikes near Kobane on Monday and Tuesday.

Several armed vehicles, anti-aircraft artillery, a tank and a jihadist "unit" were damaged or destroyed, it said.

At least 412 people, more than half of them jihadists, have been killed in and around Kobane since IS began its assault in mid-September, according to the Syrian Observatory for Human Rights, a Britain-based monitoring group.

Turkish President Recep Tayyip Erdogan warned that the strategically important town was "about to fall", saying a ground operation was needed to defeat the militants.

"I am telling the West -- dropping bombs from the air will not provide a solution," he said.

Iran, which unlike the West supports President Bashar al-Assad's regime, criticised the "passivity of the international community" in the face of the IS offensive.

Kurdish militiamen in Kobane waged fierce street battles with the advancing jihadists, who pierced the town's defences on Monday.

The defenders have vowed to "fight to the last person," said Kobane activist Mustafa Ebdi.

Idris Nahsen, a Kurdish official still in the town, said by telephone: "We need help from the international community. Either we finish them (IS) or they will finish us."

- Town turned battlefield -

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.

"There are no more civilians in Kobane. It's just a battlefield," said resident Faruq Hajji Mustafa, who fled the town, also known as Ain al-Arab, on Monday.

But a spokesman for the main Kurdish fighting force, the People's Protection Units (YPG), said some civilians had declined to leave their homes.

"My mother, for instance, refused," Polat Can told AFP by Internet.

"I am fighting with my two brothers because it's a matter of life and death. There are hundreds of sisters, brothers, fathers and sons who are fighting side by side."

The United States and its allies have launched nearly 2,000 air raids against jihadists in both Iraq and Syria in an attempt to stop their advance.

The Netherlands said its F-16s had carried out their first strikes on IS in Iraq as part of the US-led campaign, targeting armed vehicles shooting at peshmerga Kurdish fighters.

- Refugees and bodies -

The battle for Syria's Kobane has prompted some 200,000 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 frontier overnight, both civilians and Kurdish fighters.

Seven bodies were also carried across.

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

In Istanbul, protesters clashed with Turkish police in a new show of anger over the government's inaction, with tear gas and water cannon used to disperse several hundred demonstrating Kurds.

One person was killed during similar clashes in the southeastern city of Mus.

IS, an extremist Sunni Muslim organisation, has taken advantage of the chaos unleashed by Syria's several-sided civil war to capture large parts of the country, as well as of neighbouring Iraq.

The group has been accused of carrying out widespread atrocities, including mass executions, abductions, torture and forcing women into slavery.

In northwestern Syria, a rival extremist organisation to IS -- the Al-Qaeda-affiliated Al-Nusra Front -- abducted a priest and 20 other Christians on Sunday night, the Franciscan Order said.

IS sparked outrage at the weekend with the release of a video showing the beheading of British aid worker Alan Henning, one of several Western hostages killed by the group.