Ukraine said on Sunday that Russia holding a referendum in occupied Ukrainian territory would have no legal basis and would face a strong response from the international community, deepening its global isolation.

The Luhansk region in eastern Ukraine could hold a referendum soon on joining Russia, its local leader was quoted as saying.

"Fake referendums in the occupied parts of Ukraine are null and void. No country in the world will ever recognize the forceful change of Ukraine's internationally recognized borders," Ukrainian foreign ministry spokesperson Oleg Nikolenko said in a tweet.