The details of the Turkish grounding of a Syrian passenger plane earlier this week remain murky, but that hasn't stopped Turkey and Syria from trading accusations.
UN investigators said they have strong evidence of human rights abuses committed by both sides of the conflict in Syria, which has left more than 19,000 people, mostly civilians, dead.
A no-fly zone imposed by NATO and Arab allies helped Libyan rebels overthrow Muammar Qaddafi last year. But the West has shown little appetite for any Libya-style action in Syria.
Such high-level defections have been rare so far. But if they become more frequent, they could cause Assad's regime to crumble from within.