Ukrainian utility crews were working to repair new and significant damage to the country’s energy grid, officials said on Saturday, after Russia launched a swarm of Iranian-made attack drones overnight on the heels of a huge barrage of cruise missiles, antiaircraft missiles and drones on cities across Ukraine.
The attacks caused serious damage to Ukraine’s already battered power grid, which Russia has repeatedly targeted in what military analysts say is a strategy of plunging the country into cold and darkness to lower morale.
The strikes, the first heavy aerial assault in weeks, occurred as fighting on the ground has intensified, with Ukrainian officials saying that Russian forces are mounting a major new push to seize control of the entire Donbas region of eastern Ukraine.
Air-defense systems destroyed 20 of the Shahed-136 drones from 6 p.m. to midnight, the Ukrainian Air Force said in a statement early Saturday. But three energy facilities in the Dnipro region of southeastern Ukraine were hit, including one in Kryvyi Rih for the second time in a day.
The drone attack occurred after Russian forces fired more than 100 missiles in a day of strikes across Ukraine, in what both Russia’s Defense Ministry and the Ukrainian air force described as a “massive” assault. Twelve people were injured across the country, according to Ukraine’s State Emergency Service, and the state-owned power utility said that several thermal and hydroelectric power plants had been badly hit.
The company, Ukrenergo, on Saturday called the situation “difficult but under control,” saying that power rationing had been put in place in some areas and that repair work was continuing.
Kharkiv, in northeastern Ukraine, was hard-hit, according to officials. The head of the regional military administration, Oleh Syniehubov, on Saturday cited “extensive” damage to infrastructure and said that emergency power shutdowns would be in place for “several days.”
The attacks also disrupted operations at Ukraine’s nuclear power plants, according to the United Nations’ nuclear watchdog. It said late Friday that “instability in the electrical grid” had caused a reactor unit at the Khmelnytskyi plant in western Ukraine to shut down, and that the power output at two others plants had been reduced as a precautionary measure.
As the war nears its first anniversary, Russia has been pouring troops and equipment into eastern Ukraine, in the early stage of what Ukrainian and Western officials say is expected to be a major offensive.
Ukraine’s Western allies have been rushing to provide more powerful weapons so that Kyiv can mount its own offensive. The government of President Volodymyr Zelensky has reiterated its calls for even more arms — and faster delivery.
Mr. Zelensky said he had received “good signals” from allies when he pressed his case for heavier weapons on a rare international trip this past week to London, Paris and Brussels.
“This applies both to long-range missiles and tanks, and to the next level of our cooperation — combat aircraft,” he said on Friday in his nightly address. “But we still need to work on this.”
John F. Kirby, a White House spokesman, on Friday predicted that the coming weeks and months would be “difficult and critical” for Ukraine. He said that while he had yet to see a major new offensive take shape, “we’re anticipating that and, frankly, so are the Ukrainians.”
The United States believes that President Vladimir V. Putin of Russia will “take advantage” of the winter months to “restock, resupply, rearm” for what could be renewed offensive operations in the spring, Mr. Kirby told a news briefing on Friday. “As the weather improves, the fighting will probably get more vicious,” Mr. Kirby said.
In recent weeks, some of the fiercest fighting has centered on the Russian-occupied city of Kreminna and the Ukrainian-held city of Bakhmut, which are about 30 miles apart in the Donbas region.
Ukraine’s military said on Saturday that Bakhmut remained the main focus of Russian forces, with 124 strikes and 54 “clashes” in the area over the past day. Moscow sees the city, which it has been bombarding since the summer, as a crucial step toward its goal of taking all of Donbas.
Bakhmut’s strategic value, military analysts say, is as a crossroads for some of the region’s highways. Capturing the city would not guarantee that Russia could make major advances in the east, but it would better position its forces to do so.
The battle for the city has been one of the bloodiest of the war, billed as a “meat grinder” for the heavy casualties suffered on both sides. Russia’s efforts there were for some time largely spearheaded by fighters from the Wagner private military company, which has recruited prisoners into its ranks. Its founder, Yevgeny V. Prigozhin, is a close associate of Mr. Putin’s and is seen as wanting a victory in Bakhmut to boost his political standing in Russia.
But with the fight grinding on, and Moscow eager to notch its first significant battlefield victory in months, the Kremlin in recent weeks has been flooding the area with troops. Analysts say that regular Russian forces are increasingly prominent around Bakhmut.
In a rare video interview released on Friday, Mr. Prigozhin predicted that it could be some time before Moscow achieves its military aims in the Donbas region. “We will need to work for one and a half to two years,” he told Semyon Pegov, a Russian military blogger.
Mr. Prigozhin also urged patience when it came to Bakhmut.
“It is probably too early to say that we are close,” Mr. Prigozhin said, noting that Ukraine’s military had been sending in additional units. But, he added, “we are managing very well.”
Ivan Nechepurenko contributed reporting.