The negotiations were mediated by Turkey after nudging by the United Nations, according to the sources who spoke to Reuters on condition of anonymity due to the sensitivity of such talks.

A deal was reached in March “to ensure the safety of merchant shipping in the Black Sea”, and though Ukraine did not want to sign it formally, Kyiv gave its assent for Turkish President Tayyip Erdogan to announce it on March 30, the day before critical regional elections, the sources said. “At the very last minute, Ukraine suddenly pulled out and the deal was scuttled,” said one of the sources.