As if to accentuate that dependence, traffic signals in Crimea suddenly darkened on Wednesday morning, local news media reported, and telephone coverage was lost across the entire peninsula. Russian military units stationed on the peninsula, which have been reinforced since the annexation, were forced to switch to alternative power sources but suffered no loss to military readiness, the Russian Defense Ministry said in a statement on Wednesday.

Vladimir Demchishin, the Ukrainian minister of coal and energy, confirmed during a meeting of the government that energy deliveries to Crimea had been halted intentionally, saying that the peninsula had exceeded consumption limits.

“The Crimean Peninsula for a considerable period of time this morning was cut off,” Mr. Demchishin said, adding that power supplies had since been resumed to the peninsula, which has a population of more than two million. “We hope that consumers in Crimea will adhere to the limits which were agreed upon.”

Ukraine is confronting an energy crisis as supplies of coal from the belligerent Donetsk and Luhansk regions have been disrupted by the conflict there, and rolling blackouts in other Ukrainian regions and in Crimea have occurred on several occasions.

Mr. Putin, in a speech this month, declared Crimea “sacral” and has given priority to projects to maintain and improve quality of life on the peninsula. But Russia has no direct land access to Crimea, and plans for a bridge to be built from Russia across the Kerch Strait, where ferry traffic is regularly disrupted by bad weather, will be completed at the earliest in 2018.

The blackout occurred just hours before negotiators were set to meet in Minsk, Belarus, to continue talks on a settlement to the conflict in southeast Ukraine, where a shaky cease-fire has held since early September despite almost daily reports of shelling from the region.

The meeting of the “contact group,” the first since September, comes as the search for a political solution to the conflict and attempts to delineate a cease-fire line have stalled.