Unknown people presumed to be Ukrainian nationalists knocked out all four of the main electricity lines running through the Kherson region — the first two were severely damaged on Friday and two more by explosions just after midnight on Sunday morning.

Officials in Ukraine said some power could be restored in 24 hours and all four destroyed pylons restored within two or three days, but they said unidentified demonstrators were preventing repair crews from getting access to the site.

Six repair brigades had arrived in the area and were ready to start work, Yuri Kasich, of Ukrenergo, the state agency that runs the power grid, was quoted as saying by Ukrainian news services. Mr. Kasich declined to say who was causing the problem, but he said workers had yet to start the repair work.

The government in Crimea imposed rolling blackouts on most residential neighborhoods and announced that it had enough fuel on hand for emergency generators to keep them running for a month.