Three Russian flags were reported flying at one of the entrances to Ukraine’s naval headquarters in the Crimean port of Sevastopol on Wednesday, suggesting that at least some of the base was under the control of pro-Russian forces.

The Interfax news agency quoted a defense official as saying on Wednesday Russia’s military started large-scale aviation exercises in western regions, indicating the exercises were taking place mostly in northwestern regions that do not border Ukraine. Russia’s top crude oil producer Rosneft says it has no plans to cut its activity in Ukraine.