Crimea declared a state of emergency on Sunday after its main electricity lines from Ukraine were blown up, leaving the Russian-annexed peninsula in darkness after the second such attack in as many days.
More than 1.6 million people are without power, water supplies to high-rise buildings have stopped and cable and mobile Internet is down.
The electricity feed from Ukraine was cut at 00:25 am (2225 GMT), the Crimean branch of Russia\’s emergency situations ministry said in a statement.
Crimea still depends on Ukraine for its electricity even after its annexation by Russia in March last year, a move which paved the way for the uprising in eastern Ukraine that has now killed more than 8,000 people.
The Black Sea peninsula produces only 30 percent of its own energy needs, according to the regional government.
"As of 1 pm (1000 GMT), 1,641,000 people have been left without electricity," and 150 schools have no power, Russia\’s energy ministry said.
So far, Crimea has enough fuel to keep the gas and diesel-powered generators it has running for 29 days, the Russian authorities said.
An explosion on Saturday in Ukraine\’s Kherson region bordering Crimea cut the two working power lines to the peninsula, the state energy company Ukrenergo told Interfax-Ukraine news agency.
Two of the total four power lines had already been downed Friday in separate blasts.
In the port city of Sevastopol, electricity was cut off completely at 2:00 am, although different districts have since had brief rolling periods of power, an AFP journalist reported.
"I had no electricity all night. These useless officials can\’t run the city and they still haven\’t built a local power station," said 49-year-old resident Konstantin.
"It\’s not the first time Ukraine has cut off electricity to Crimea, we are already used to power cuts and stock up on batteries," added Oleg, 56.
"The problem is the fridge keeps going off."
After the first attack on Friday, Ukrenergo posted pictures of a downed pylon and one with a hole blown through it.
"The nature of the damage shows that it took place as a result of shelling or the use of explosive devices," it said.
The head of the anti-narcotics department of Ukraine\’s interior ministry, Ilya Kiva, who was at the scene, wrote on Facebook: "The pylons have just been blown up!!!"
The identity of the attackers is not known.
"The investigation is ongoing. So far there are no hypotheses, the investigators are working," Ukrainian interior ministry spokeswoman Nataliya Stativko told AFP.
Crimea\’s leader Sergei Aksyonov suggested Ukraine was involved in the blasts and said Crimea\’s prosecutors have opened their own criminal probe.
"I think Ukraine isn\’t looking for (the attackers). Its agencies may have done this themselves. I consider this action was agreed upon," Aksyonov told Moscow\’s Govorit Moskva radio.
Russian senator Franz Klintsevich called the attacks "an act of terrorism."
"Blowing up the power lines… close to the Crimean border has practically cut off the whole peninsula. That\’s a real act of terrorism," he told RIA Novosti news agency.
Crimean Tatars, an ethnic group native to the peninsula who oppose Russian rule, have been holding protests at the site of the broken power lines since Saturday, calling for a blockade of Crimea to protest at the jailing of dozens of activists.
"We want to end the occupation of Crimea," said Refat Chubarov, one of the leaders of the community.
He declined to comment on whether activists could have been involved in the explosions, saying: "I wasn\’t there."
Crimea experienced several total power cuts last winter, attributed by the authorities to repairs and technical problems, but seen by residents as deliberate pressure from Ukraine.
Russia plans to build two gas-powered power stations in Crimea which would burn gas piped from the mainland, but these are still at the planning stage.