Syrian human rights groups have called on the world to save the embattled Syrian Kurdish town of Kobani from falling into the hands of the Islamic State group, as new US-led air strikes targeted the extremists near the town.

The strikes are part of a wave of US-led coalition bombing this week that aims to prevent IS fighters from capturing the town.

An activist group said the strikes had killed at least 45 militants since late Monday, forcing them to withdraw from parts of Kobani.

The appeal by human rights groups came after IS fighters - despite the air strikes - pushed into parts of the town on the Turkish border, also known by its Arabic name of Ayn Arab.

Kobani has been under the onslaught of IS since mid-September when the militants launched their offensive in the area, capturing several Kurdish villages around the town and again bringing Syria's civil war to Turkey's doorstep.

The fighting has forced more than 200,000 of the town residents and villagers from the area to seek shelter across the frontier in Turkey. Activists also say that more than 400 people have been killed in the fighting.

Today planes believed to be with the US-led coalition bombed IS positions near Kobani. One air strike, visible from the border, hit a hill and an open space near the town.

The Britain-based Syrian Observatory for Human Rights said the strikes targeted IS fighters east of Kobani.

Since Monday night, the strikes have killed 45 IS fighters in and around Kobani, targeted 20 separate locations held by the extremists and destroyed at least five of their vehicles, the Observatory said.

The air strikes also forced IS fighters to withdraw from several streets they had controlled earlier, added the Observatory, which tracks the Syrian conflict through a network of activists on the ground.

Meanwhile, an attack apparently carried out by Kurdish fighters inside the town destroyed a mosque minaret which IS had used as an outlook, activists said.

Heavy gunfire was heard from inside the town in a sign of fresh clashes today. The Observatory said most of the fighting was in the town's Kani Arban neighbourhood.

In their appeal, seven rights groups - including the Kurdish Organisation for Human Rights and the Human Rights Organisation in Syria - said the IS offensive on Kobani and "inhuman practices and measures have taken a clear form of persecution and ethnic cleansing".

The statement also said that the fighting over Kobani has displaced nearly 280,000 people who fled fearing "killings, executions, throat slitting, beheadings, mayhem and kidnapping of women and children".

IS has conquered vast areas of Syria and Iraq, declaring a self-styled caliphate governed by its strict interpretation of Islamic law, or shariah. The militants have massacred captured Syrian and Iraqi troops, terrorised minorities and beheaded two US journalists and two British aid workers.

Last week, IS fighters also beheaded nine Kurdish fighters, including three women, captured in clashes around Kobani.

Also today, a Kurdish activist said he was detained by Turkish authorities with 157 residents from Kobani and other activists shortly after they crossed into Turkey three days ago. Mustafa Bali said the detainees include 33 women, nine children and the rest were mostly elder men.

Mr Bali said the activists were to escort Kurdish civilians from Kobani to safety in Turkey, then cross back.

"They allowed us to cross and once we were in Turkey they detained us," Mr Bali said.

The Syrian human rights groups also criticised Turkey, saying it was "preventing and hindering the entrance of Kurdish refugees fleeing Syria's northern border from the brutality and terrorist acts" of the Islamic State group.

The Pentagon said some IS militants had left the area as a result of the coalition air strikes, but the town could still fall.

Rear Admiral John Kirby, Pentagon press secretary, says the US is doing everything it can from the air to try to halt the IS momentum against the town, but added that air strikes alone will not save the city and there are no plans to send US ground forces in. He says other towns are also at risk.

There were air strikes at six locations around Kobani yesterday, and others earlier this week. He said there are mixed reports about how many IS militants pulled back.

US secretary of state John Kerry said he would consider supporting a buffer zone inside Syria to bolster Turkish borders against Islamic militants and protect it from being overwhelmed by refugees.