A Russian humanitarian convoy will not be allowed to pass through the Kharkiv region's territory, Ukrainian Interior Minister Arsen Avakov wrote in Facebook.
"No 'humanitarian convoy' from [Russian President Vladimir] Putin will be admitted through the Kharkiv region's territory. A provocation by the cynical aggressor on our territory is unacceptable," Avakov said on Wednesday, adding that his words amounted to an official statement.
A Russian convoy of up to 280 trucks carrying humanitarian aid has reportedly left for Ukraine August 13.
Russian officials said the trucks were carrying 2,000 tons of aid, from baby food to sleeping bags.
The International Committee of the Red Cross said it had no information on what the trucks were carrying or where they were going.
Ukrainian and Western officials have voiced concerns that Russia could use the pretext of humanitarian aid to send troops into eastern Ukraine where government forces are fighting pro-Russian separatists.