The disagreement, played out in rival tweets, is the latest consequence of U.S. President Donald Trump's Dec. 19 decision to withdraw U.S. troops from Syria, potentially leaving the Kurdish militia under threat as Turkey weighs a new offensive there. U.S.-Turkish relations have been strained by U.S. support for the Kurdish YPG, which Turkey views as a terrorist group and an extension of the outlawed Kurdistan Workers Party (PKK) that has for decades waged a separatist insurgency in Turkey. The Kurdish YPG has been a U.S. ally in the fight against the Islamic State (ISIS) jihadists and it controls swaths of northern Syria.