Russia's siege of the city of Mariupol has further complicated the negotiation process in the war in Ukraine and it is hard to say when direct talks might resume, Ukrainian negotiator Mykhailo Podolyak told Reuters on Tuesday.

Podolyak said in a written response to questions from Reuters that he believed Russia was banking on strengthening its positions through a new offensive it has launched in eastern Ukraine.

"Obviously, against the backdrop of the Mariupol tragedy, the negotiation process has become even more complicated," he said of the southern port city where Russia has given the last Ukrainian defenders holed up in a steel works an ultimatum to surrender by noon (0900 GMT).

(Reporting by Natalia Zinets, Editing by Timothy Heritage)