The report said Ukraine wants a gradual increase in the tariff to 21 euros ($23.11) per tonne of oil transported from Aug. 1, up from the current rate of 13.60 euros.

The Argus pricing agency and market sources said the rate could rise by 25% initially to 17 euros per tonne from June 1 and by another 23.5% to 21 euros from Aug. 1, Kommersant reported.

Ukrainian oil pipeline operator Ukrtransnafta and the Russian Energy Ministry did not reply immediately to emailed requests for comment.

($1 = 0.9086 euros)

(Reporting by Vladimir Soldatkin; Editing by David Goodman)