Islamic State forces have made new gains in Kobani, now controlling about 40 percent of the Syrian town of Kobani on the Turkish border and might well capture it, Deputy US National Security Adviser Tony Blinken has said.

“I don't know what's going to happen because again in the absence of any ground force there, it is going to be difficult just through air power to prevent ISIL (IS) from potentially taking over the town," Blinken told reporters at a briefing in London on Friday.

This information is also confirmed by the the Syrian Observatory for Human Rights.

"They have taken at least 40 percent (of the town)," the head of the monitoring group, Rami Abdulrahman, said by telephone as reported by Reuters.

Islamic State fighters were now in almost complete control of the "security quarter," which is home to the administrative buildings used by the local government, he said.

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The IS militants have seized control over some of the eastern areas of the town and smaller areas in the south of Kobani, the Syrian Observatory for Human Rights said.They have seized the Kurd headquarters also, a monitoring group said.

"They are trying to advance on the crossing from the east ... but the YPG [fighters] are resisting them," Ocalan Iso, the deputy head of the Kurdish forces defending Kobani, told Reuters.

Fighting is also going on between IS and Kurds near a building used by Kurdish internal security forces, according to Kurdish military official. He denied any major advance by IS, though.

Ocalan Iso, deputy head of the Kurdish forces, said Islamic State was still conducting air strikes in the town center with mortars.

"There are fierce clashes and they are bombing the center of Kobani from afar," he told Reuters by telephone.

Thousands of people "will most likely be massacred" if Kobani falls to Islamic State fighters, UN envoy Staffan de Mistura said on Friday.

The UN envoy compared possible Kobani population fate with one of Bosnian town of Srebrenica, where 8,000 Muslims were killed by Serbs in 1995, while UN peacekeepers failed to protect them.

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A total of 200,000 people have allegedly fled the region over the last three weeks, horrified by IS’s rapid advance. The radical Islamist forces used heavy artillery to attack residential areas.

On Friday, fighting between IS and Kurdish forces in Kobani could be heard across the border.

The US-led coalition has also intensified airstrikes over the last two days around Kobani in response to the IS offensive.

Kurdish officials have been urging Ankara to allow weapons and fighters to flow into Kobani through Turkey. However, Turkish officials aren’t keen to help the town's Kurdish defenders, as they have strong connections with the PKK, considered a terrorist group in Turkey, the US and Europe.

Turkish officials refuse to intervene unilaterally, as they are concerned they would become involved in Syria’s bloody war.

In Turkey, the situation in Kobani triggered violent clashes between rival groups in over a third of the country’s provinces, with 31 killed, according to Interior Minister Efkan Ala, Reuters reported.

Over a thousand people have also been detained.

Earlier this week, 25 people were killed after pro-Kobani rallies turned into bloodshed, local media reported.

The anger over Kobani revealed the decades-long conflict between supporters of the Kurdistan Workers' Party (PKK) and Turkey, which is strongly against the PKK. Violent conflict between the two sides ended about a decade ago.

PKK has been waging a war against the Turkish government for 30 years, demanding more autonomy.