ANKARA (Reuters) - Turkish President Tayyip Erdogan said on Saturday that a major military operation was underway in the Syria s northwest province of Idlib, which Free Syrian Army rebel groups earlier said they were preparing to enter with Turkish backing.  There is a serious operation in Syria s Idlib today, and this will continue,  Erdogan told members of his AK Party in a speech.  Much of Idlib is currently controlled by an jihadist-led alliance of fighters.  We will never allow a terror corridor along our borders in Syria,  Erdogan said.  We will continue to take other initiatives after the Idlib operation.  