Turkish President Recep Tayyip Erdogan has lashed out at the US over its support for Syria`s main Kurdish group.The failure to recognise the Democratic Union Party (PYD) as a terrorist group was creating a "sea of blood", he said, reports BBC.Turkey says the PYD, on which the US relies to battle so-called Islamic State in Syria, is an offshoot of the banned Kurdistan Workers` Party (PKK).Mr Erdogan`s comments come as Turkey faces pressure to allow in 30,000 Syrian refugees stranded on its border.The refugees have fled an offensive by Syrian government forces and Iranian-backed militias, supported by Russian air strikes, on rebel-held areas around the divided northern city of Aleppo.More than 500 people, including dozens of civilians, have been killed since the assault began 10 days ago, according to the Syrian Observatory for Human Rights, a UK-based monitoring group.Medecins Sans Frontieres meanwhile warned that the fighting was placing extreme pressure on the already devastated healthcare system in the border town of Azaz.MSF`s head of mission for Syria, Muskilda Zancada, warned that displaced people, including young children and the elderly, could be stuck living in the open in freezing conditions, with severe effects on their health.Turkey has already taken in more than 2.5 million Syrian refugees over the past five years and says it will continue to do so in a "controlled fashion".