Multiple demonstrations have been held over the last few days in the Russian-occupied cities of Kherson, Melitopol and Berdyansk, according to UK intelligence.
The Ministry of Defence said Russia may try to stage a “referendum” in Kherson as part of plans to legitimise the area as a breakaway republic.
During protests in the city yesterday, Russian forces reportedly fired warning shots to disperse peaceful protesters.
Russia has already recognised the separatist-controlled regions of Donetsk and Luhansk in eastern Ukraine as breakway republics, but the West has refused to do so.
Russia has also reportedly installed its own mayor in Melitopol following the alleged abduction of his Ukrainian predecessor last week, while the mayor of Dniprorudne has also allegedly been abducted.