As many as 70,000 Syrian Kurds have poured into Turkey since Friday fleeing an offensive by Islamic State jihadists in northeastern Syria, the U.N.'s refugee agency said Sunday.

The UNHCR "is stepping up its response to help Turkey come to the aid of an estimated 70,000 Syrians crossing into Turkey", most in the past 24 hours, the agency said in a statement.

Islamic State jihadists were closing in on Syria's third largest Kurdish town Sunday after their capture of surrounding villages sent tens of thousands of refugees streaming into Turkey, a monitoring group said.

IS fighters were within just 10 kilometers (six miles) of the strategic border town known as Ain al-Arab in Arabic and Kobane in Kurdish, the Syrian Observatory for Human Rights said.

Some 45,000 Syrian Kurds fleeing advancing Islamic State jihadists have poured across the border into Turkey since Ankara opened up its southern frontier on Friday, the country's deputy prime minister said.

"As of now, 45,000 Syrian Kurds have have crossed the border and entered the Turkish soil from eight entrance points," Numan Kurtulmus told reporters on Saturday.

Blamed by some for prompting the rise of the Islamic State insurgency, Turkey has finally taken steps to tighten its borders with Iraq and Syria but is still disappointing the West over its low-key role in the anti-IS fight.

Western diplomats accuse President Recep Tayyip Erdogan's Islamic-rooted government of failing to show wholehearted support for the battle against IS militants who control swathes of Iraq and Syria, although Turkish officials bitterly reject these claims.

Dozens of Turkish nationals held hostage by Islamic State jihadists in northern Iraq for more than three months have been released and brought to Turkey, Turkish Prime Minister Ahmet Davutoglu said on Saturday.

"Early in the morning our citizens were handed over to us and we brought them back into our country. At 5:00 am (0200 GMT) they entered the country," Davutoglu told reporters during an official visit to Azerbaijan, adding that all were in good health.

Turkey on Friday reopened its border with Syria to Kurds fleeing Islamic State (IS) militants, saying a "worst-case scenario" could drive as many as 100,000 more refugees into the country.

Groups of visibly exhausted Syrian Kurds, most of them women and children who had fled their homes on foot, were shown on live television crossing into the southeastern Turkish village of Dikmetas, under tight security.

The families of the troops abducted by Syria-based jihadist groups on Thursday urged the kidnappers to stop threatening to kill more soldiers, as highly-informed sources said negotiations have made “slow progress.”

Prime Minister Tammam “Salam told us that the negotiations have not stopped and that the demands received by the government need some time,” Jamaa Islamiya member Ahmed al-Ayyoubi said on behalf of the families after a meeting with the premier.

Jihadists from the Islamic State group using heavy weapons have seized a string of villages around Ain al-Arab as they close in on Syria's third largest Kurdish town, a monitor said Thursday.

Turkey's military is mulling the prospect of establishing a buffer zone along its border with Syria and Iraq amid an escalating threat posed by Islamic State extremists, President Recep Tayyip Erdogan was quoted as saying on Tuesday.

Turkey would welcome exiled leaders of Egypt's outlawed Muslim Brotherhood who have come under pressure to leave Qatar, President Recep Tayyip Erdogan has said.

A Brotherhood official said on Saturday that several members of the group were relocating after Qatar came under enormous pressure from other Gulf Arab states to cut support for the Islamist group.