Deposed Ukraine President Viktor Yanukovych has called Russia's annexation of Crimea a tragedy.
In his first interview since fleeing to Russia, Mr Yanukovych said he hoped Crimea would one day become part of Ukraine again.
Mr Yanukovych fled Kiev in February after months of street protests.
"Crimea is a tragedy, a major tragedy," he said in the city of Rostov-on-Don in southern Russia.
The BBC reports he said he would try to persuade President Vladimir Putin to return Crimea to Ukraine.
"We must set such a task and search for ways to return to Crimea on any conditions, so that Crimea may have the maximum degree of independence possible... but be part of Ukraine."
Mr Yanukovych said had he remained in power, he would have tried to prevent the referendum, calling it a "form of protest" against Ukraine's new pro-Western leaders.
Unrest in Ukraine began late last year when Mr Yanukovych rejected an agreement of association with the EU in favour of closer ties with Russia.
The interim government in Kiev that took power after Mr Yanukovych fled has scheduled a presidential and some mayoral elections for 25 May.
The BBC says Russia's actions in Ukraine have caused concern in Estonia, Latvia and Lithuania, which were part of the Soviet Union during the Cold War.