Crimea has declared a state of emergency after its main electricity lines from Ukraine were blown up, leaving more than 1.6 million people on the disputed Russian-annexed peninsula in darkness after the second such attack in as many days.
It was not immediately clear who had blown up the pylons, but a Russian lawmaker said it was an "act of terrorism" and implied Ukrainian nationalists were to blame.
Two transmission towers in Ukraine were damaged by explosions early Sunday and another two on Friday, the Russian Energy Ministry said.
By late Sunday electricity supplies had been restored to more than a quarter of the population, largely in the major cities, through the use of mobile gas turbine generators. But water supplies to many high-rise buildings remained stopped and cable and mobile Internet is down.
Ukrainian activists calling for an economic blockade of the Black Sea peninsula tried to prevent repair work on Saturday, but retreated after clashes with police.
Crimea was annexed by Russia last year but depends on Ukraine for most of its electricity supplies.
Ukrainian police said it was not immediately clear who was responsible for the attacks.
Ukraine's UNIAN news agency first reported Friday that two of the four main power lines had been disabled following an explosion of an unidentified device.
Separately, Ukraine's Channel 5 television reported that Ukrainian police had surrounded a group of Tatar activists near the downed lines. The report, quoting Lenur Islyamov, the head of a group advocating the blockade of Crimea, described the situation at the site of the downed power lines as "tense."
The Russian parliament voted overwhelmingly in March 2014 to annex the largely Russian speaking territory, just weeks after pro-Western Ukrainian protests in Kyiv forced Russia-leaning President Viktor Yanukovych from office.
Weeks later, pro-Russian separatists in eastern Ukraine launched a rebellion against Kyiv's rule that triggered a series of trade and travel sanctions against key Russian officials close to President Vladimir Putin.
Those sanctions are due to expire in January. But Reuters news agency, reporting Saturday, said Western leaders meeting on the sidelines of a G-20 summit in Turkey have agreed to extend the sanctions until July 2016.
The United Nations said in September that nearly 8,000 people, most of them civilians, have been killed in the conflict.