Turkey lashed out at the UN and the US as it is facing mounting pressure to allow in tens of thousands of Syrian refugees that fled a Russian-backed regime offensive on Aleppo and are now stranded on its southern border.

First, Ankara responded angrily at the UN refugee agency (UNHCR) which urged the government to let in all civilians displaces by fighting. President Recep Tayyip Erdogan fired back accusing the UN body of being useless, pointing out that Turkey is already hosting three million refugees and has contributed more money that it received to fund humanitarian assistance.

"What does the UN say? 'Open your border to the refugees.' What are you for then? What is your use? Is it that easy?" Erdogan lambasted. "We have taken three million Syrians and Iraqis into our home until now. How many did you take? Which country took them in?"

Later, Prime Minister Ahmet Davutoglu piled it on, attacking the UN Security Council as "two-faced" for failing to take action to stop Russian bombardments that are causing the refugees to flee, AP reported. Russia is a permanent member of the Security Council with veto power.

Davutoglu even argued that allowing Syrians fleeing the war into Turkey would indirectly contribute to what he said was the "ethnic cleansing" carried out by the regime of Bashar al-Assad. An estimated 31,000 people have fled Aleppo in the past few days.

Earlier Erdogan had ratcheted up his already vocal criticism of the US strategy over the Syrian conflict, blaming Washington's support of Kurdish militants in the north for the carnage raging across the border. Ankara has been particularly angered at a visit by US envoy Brett McGurk to Kobane to meet representatives of the Kurdish Democratic Union Party (PYD), which Turkey says is affiliated to the Kurdistan Workers' Party (PKK).

The PKK is listed as a terrorist organisation both in the US and Europe and is leading an armed insurgency against the Turkish government, which has responded with a violent crackdown condemned by rights groups in the majority-Kurdish areas of the country's south-east.

"You failed to know (these groups). That's why the region is drenched in blood," Erdogan said, a day after summoning the US ambassador. Meanwhile. the PYD's armed wing, the YPG, has exploited the regime offensive in Aleppo to capture a military air base form the rebels.