Security forces are surrounding Russian facilities in Ukraine amid anger over the Ukrainian government’s refusal to allow ordinary Russians to vote for president.
Ukrainian police are guarding the Russian Embassy in Kiev and consular offices in Odessa and other cities.
The Ukrainian government announced that only Russian diplomatic officials would be allowed to cast ballots in Sunday’s vote, which Vladimir Putin is set to win.
Millions of ethnic Russians live in Ukraine but the number of registered Russian voters in Ukraine is unclear.
Ukraine is protesting voting in Crimea, annexed by Russia from Ukraine four years ago. Ukraine is also angry over Russian support for separatists in eastern Ukraine, where a deadly conflict continues.
Russian authorities are appealing to the United Nations and Council of Europe to intervene, according to Russian news agencies.