Tens of thousands of Syrian Kurds flooded into Turkey on Saturday, fleeing an onslaught by the jihadist Islamic State group that prompted an appeal for international intervention.

The massive influx came as 46 Turks kidnapped by IS jihadists in Iraq in June were freed and returned home for emotional reunions with their families.

Turkish Deputy Prime Minister Numan Kurtulmus said more than 60,000 Syrian Kurds had crossed into the country since the border was opened on Friday.

The exodus was prompted by intense clashes between IS and Kurdish fighters trying to hold off the jihadists' assault on the town of Ain al-Arab, known as Kobane by the Kurds.

It is the third-largest Kurdish town in Syria and a strategic prize because it lies on the border with Turkey in northern Aleppo province.

Since Tuesday night, IS fighters have been advancing on the town, hoping to seize it and secure their control over a large swathe of Syria's northern border with Turkey.

The group has seized at least 63 surrounding villages in a lightning offensive, although the Syrian Observatory for Human Rights, a Britain-based monitor, said 18 IS fighters were killed in clashes overnight.

It said 13 jihadists were killed on Saturday, and that 25 Kurdish fighters have been killed since Tuesday.

On Saturday, the Observatory said 300 Kurdish fighters had entered Syria from Turkey to reinforce the Syrian Kurdish People's Protection Units (YPG) fighting IS.

- Children, elderly flee -

People of all ages were among those seeking shelter in Turkey, including a child clutching a sibling's hand as they fled across the dusty border and an elderly wheelchair-bound woman helped by relatives.

"The IS came to our village and threatened everyone. They bombed our village and destroyed all the houses. They beheaded those who chose to stay," said Mohammed Isa, 43, who left with his family of seven.

Turkish forces cut the barbed wire along the border to allow the refugees to enter while soldiers and aid workers handed out food and water.

The jihadists' advances have prompted calls from Syria's opposition and Kurdish officials for international action, with one leader warning of "ethnic cleansing".

The United States has organised a coalition of countries to battle IS jihadists who have declared an Islamic "caliphate" in parts of Syria and Iraq and carried out atrocities including beheadings and crucifixions.

American warplanes have launched a total of 183 air strikes across Iraq, targeting IS vehicles, checkpoints and outposts.

US President Barack Obama plans to make his case against IS at the UN General Assembly next week in a bid to garner more international support.

The Syrian opposition National Coalition urged international air strikes to "stop mass atrocities" if IS advances into Ain al-Arab.

"Air strikes are needed to help opposition forces protect vulnerable civilians," the coalition's US representative Najib Ghadbian said.

And Salih Muslim Mohamed, a leader of the Democratic Union Party (PYD), urged the West to help Ain al-Arab avoid the fate of the Iraqi town of Sinjar, which has been emptied of its Yazidi minority residents in the wake of an IS onslaught.

"Kobane is facing the most barbaric attack in its history," he warned.

"If you want to avoid an ethnic cleansing even more barbaric than that in Sinjar, you must support Kobane because the next few hours will be decisive," he added in a statement late Friday.

Obama said last week he was ready to launch strikes on IS fighters in Syria, expanding the campaign already underway in Iraq, but so far there have been none.

The Observatory reported on Saturday that IS militants had executed at least 11 Kurds, and that the fate of some 800 residents who fled their villages remained "unknown".

- Emotional return -

As Turkey dealt with the arrivals on its southern border, the government in Ankara welcomed home the 46 Turks taken hostage by IS in the Iraqi city of Mosul in June. Three Iraqis were also detained.

It was unclear how the group, abducted from Turkey's consulate in Mosul, had been freed, though President Recep Tayyip Erdogan referred to a "secret operation".

There were emotional and triumphant scenes on their return, with Prime Minister Ahmet Davutoglu cutting short a trip to Azerbaijan to greet them.

"Early in the morning our citizens were handed over to us and we brought them back into our country," Davutoglu told reporters before leaving Baku.

"There are unnamed heroes, like those who brought our citizens back to Turkey," he told cheering crowds at the airport back in Ankara.

Meanwhile the wife of a British taxi driver held hostage by IS jihadists released a statement imploring his captors to free him, saying she "cannot see how it could assist any state's cause to allow the world to see a man like Alan dying."

Alan Henning volunteered to drive a humanitarian aid convoy to Syria for a Muslim charity but was captured 10 months ago by the IS group.

burs-sah/hmn/mtp