[To match INTERVIEW GEORGIA-OSSETIA/MONITORS/]By Tulay Karadeniz and Ece Toksabay ANKARA (Reuters) - The European Union's top envoy to Turkey has resigned, EU officials said on Tuesday, in a further sign of strained relations as Brussels tries to keep a deal credited with curbing the flow of illegal migrants to Europe on track. Hansjoerg Haber's resignation comes a month after he was summoned by Turkey's foreign ministry over comments critical of Ankara's handling of the migration accord. The 28-nation EU is dependent on Turkey to enforce a deal, criticised by rights groups, that has sharply cut the number of refugees and migrants reaching Greece, giving EU leaders breathing space after more than a million arrived last year.