Estonia's Prime Minister Kaja Kallas told her nation that blackouts are possible if Russia kicks the Baltic states from the joint power grid, as she announced a snap defence readiness exercise.
"We must also be prepared for Russia might disconnect Estonia, Latvia, and Lithuania from their electricity grid", she said in a televised address on Thursday evening, according to the government website.
"It would be wise to be prepared for possible power outages — that includes public authorities, companies, and every individual", she added, describing any disruptions as "temporary".
Moscow's embassy in Estonia said on Friday that "Russia is not initiating" the exit of Baltic countries from the common grid.
About 3,000 reservists were called to an annual week-long defence exercise in Estonia on Thursday, but the prime minister said there was no immediate military threat to the country.
Ms Kallas called on Russian citizens living in Estonia to ignore any summons to fight in Ukraine.
"Do not go, because there is no turning back," she said.
Thirty years after seceding from the then-Soviet Union and 17 years since joining the EU, Baltic states Lithuania, Latvia and Estonia still depend on Russia for stable power supplies.
A €1.6 billion ($1.94bn) EU-funded project aims to disconnect the Baltic states from their common power grid with Russia and Belarus in 2025 in favour of the decentralised power system of continental Europe.
Lithuanian President Gitanas Nauseda told Reuters in June his country is ready if Russia disconnects it from the regional power grid in retaliation for blocking rail shipments of some Russian goods to Moscow's Kaliningrad exclave.
European power grid network ENTSO-E will connect to the Baltic states' grids within 24 hours if the countries were to be disconnected by Russia, helping avoid blackouts, Lithuanian power grid operator Litgrid said in July.
"If Russia disconnects us, even today, we would be ready," Litgrid's chief executive said.
"Our analysis shows that power supply would not be rationed, no serious disruptions expected".