The UN envoy for Syria has urged the international community to act to prevent the “rape and massacre" of Kobane, as US-led air attacks failed to stop ISIL storming the Kurdish-Syrian town.

Staffan de Mistura said on Tuesday that Kobane faced horrific violence under ISIL. "The world has seen what happens when a city is overtaken by the terrorist group: massacres, humanitarian tragedies, rapes, horrific violence," he said.

"The international community cannot sustain another city falling under [ISIL]. What is needed now is concrete action. The world - all of us - will regret deeply if ISIL is able to take over. We need to act now."

His comments came as ISIL continued its advance on the city, seemingly unhindered by air attacks by a US-led coalition. The black flag of the armed group was raised over three districts in the east of Kobane after fierce battles with its Syrian-Kurdish defenders.

Al Jazeera's Yilmaz Akinci, reporting from the nearby Turkish border, said that air strikes had hit the centre of the city.

"About 40 minutes after the air strikes, ISIL started to shell inside the city centre too," Akinci said.

The UK-based Syrian Observatory for Human Rights said US-led coalition is carrying out fresh air strikes near ISIL sites in Raqqa. A former base of the Syrian Regime 93rd brigade, which has been turned into ISIL headquarters and is 55km from Raqqa, has been targeted by the strikes.

Turkey's president, Recep Tayyip Erdogan, meanwhile said the city was close to capitulation and gave warning that that the US-led air campaign was not enough to stop ISIL.

"The terror will not be over ... unless we cooperate for a ground operation," Erdogan said in the eastern city of Gaziantep. "I am telling the West - dropping bombs from the air will not provide a solution."

Erdogan however stopped short of saying he would send Turkish troops into Kobane. Turkey's parliament last week authorised military action against ISIL but it has yet to begin operations.

Taha Ozhan, a senior adviser to the Turkish prime minister, told Al Jazeera that Turkey's main problem was "about the regime" in Syria.

"Without considering Assad as the source of the problem, talking about ISIL and focusing on ISIL is just one dimension of the issue," he said.

Meanwhile, pro-Kurdish demonstrators clashed with police on the Turkish side of the border and in several cities, including the capital Ankara, incensed by Turkey's inaction in the fight against ISIL.

Nine people are now confirmed dead in violence during the protests, at least two of those in crossfire during a battle between pro-Kurdish demonstrators and opponents.