Reuters reported that the European Union's top envoy to Turkey has resigned, an official from his delegation said on Tuesday, a month after he was summoned by Turkey's foreign ministry over comments critical of Ankara's handling of a landmark migration deal.

"We confirm that Haber has resigned. We are not in a position to comment on the reason at the moment," the official in the EU delegation in Ankara told Reuters.

Haber was summoned by Turkey's foreign ministry in May to complain about comments he made about the migration deal.

Turkish officials took offense at his use of an unflattering German saying, cited in local newspapers, to describe how a plan to ease visa restrictions for Turks traveling to Europe, part of the wider migrant deal, had run into problems.