Syria's Kurds, bracing for a Turkish land offensive against their autonomous northern region, face an additional threat: being squeezed by warming ties between their foe Ankara and the Assad regime.The Kurds -- an ethnic minority who live in mountainous regions across Turkey, Syria, Iraq and Iran -- have long fought for their own homeland, and Turkey brands their separatist groups "terrorists".Turkish President Recep Tayyip Erdogan has blamed Kurdish armed groups for a deadly bomb attack in Istanbul this month, an accusation they have strongly rejected.