(CNN) -- Hundreds of Kurdish fighters from Turkey have arrived in the Syrian Kurdish town of Ayn al-Arab to join a Kurdish militia group battling to hold off ISIS forces, activists said Saturday. Clashes continue in the area between the militia, called the People's Protection Unit (YPG,) and the ISIS fighters, according the London-based Syrian Observatory for Human Rights. The latest ISIS advance in Syria has brought a swath of the country's north-central Kurdish region under siege, with Kurdish leaders warning of another humanitarian crisis without international intervention. The Syrian Kurdish town of Ayn al-Arab, or Kobani as it is...