Russian complaints about a landmark deal allowing Ukraine to export grain from ports in the Black Sea are "flabbergasting" as the deal gives Moscow no role in determining where the grain goes, a Ukrainian presidential adviser said on Wednesday.

"The agreements signed in Istanbul ... concern only one issue, and that is the transfer of cargo ships through the Black Sea," Mykhailo Podolyak, an adviser to Ukrainian President Volodymyr Zelenskiy, told Reuters.

"Russia can't dictate where Ukraine should send its grain, and Ukraine doesn't dictate the same to Russia," he added.

(Reporting by Margaryta Chornokondratenko and Tom Balmforth; Writing by Conor Humphries; Editing by Jon Boyle)