KYIV, Ukraine (AP) — Russian-installed authorities ordered all residents of the southern Ukrainian city of Kherson to leave “immediately” Saturday ahead of an expected advance by Ukrainian troops waging a counteroffensive to recapture one of the first urban areas Russia took after invading the country.

In a post on the Telegram messaging service, the regional pro-Kremlin administration called on civilians to use boat crossings over a major river to move deeper into Russian-held territory, citing a tense situation on the front and the threat of shelling and alleged “terror attacks” by Kyiv.

Kherson has been in Russian hands since the early days of the invasion in February. The city is the capital of a region of the same name, one of four that Russian President Vladimir Putin illegally annexed last month and then put under Russian martial law.

On Friday, Ukrainian forces bombarded Russian positions across the province, inching closer to a full assault on its capital as they targeted pro-Kremlin forces’ resupply routes across the Dnieper River.

Russian-installed officials were reported desperately trying to turn the city of Kherson — a prime objective for both sides because of its key industries and major river and sea port — into a fortress while attempting to relocate tens of thousands of residents.

The Kremlin poured as many as 2,000 draftees into the surrounding region to replenish losses and strengthen front-line units, according to the Ukrainian army’s general staff.

The Dnieper River figures prominently in the regional battle because it serves critical functions — crossings for supplies, troops and civilians; drinking water for southern Ukraine and the annexed Crimean Peninsula; and power generation from a hydroelectric station. Much of the area, including the power station and a canal feeding water to Crimea, is under Russian control.

Kherson’s Kremlin-backed authorities previously announced plans to evacuate all Russian-appointed officials and as many as 60,000 civilians across the river, in what local leader Volodymyr Saldo said would be an “organized, gradual displacement.”

Another Russian-installed official on Saturday estimated that around 25,000 people from across the region had made their way over the Dnieper. In a Telegram post, Kirill Stremousov claimed that civilians were relocating willingly.

“People are actively moving because, today, the priority is life. We do not drag anyone anywhere,” he said, in an apparent response to Ukrainian and Western concerns about potential forced transfers by Moscow.

Ukrainian officials have urged local residents to resist attempts to relocate them, with one local official alleging that Moscow wanted to take civilians hostage and use them as human shields.

Elsewhere, hundreds of thousands of people in central and western Ukraine woke up on Saturday to power outages and periodic bursts of gunfire, as Ukrainian air defense tried to shoot down drones and incoming missiles.

Russia has intensified its strikes on power stations, water supply systems and other key infrastructure across the country, the latest phase of the war as it nears the eight-month mark.

Ukraine’s air force said in a statement Saturday that Russia had launched “a massive missile attack” targeting “critical infrastructure,” adding that it had shot down 18 out of 33 cruise missiles launched from the air and sea.

Air raid sirens blared across Ukraine twice by early afternoon, sending residents scurrying into shelters.

“Several rockets” targeting the capital were shot down on Saturday morning, Kyiv Mayor Vitali Klitschko said on the Telegram messaging service.

Similar reports were made by the governors of six western and central provinces, as well as the southern Odesa region on the Black Sea.

The presidential office said in its morning statement that five explosive-laden drones were downed in the central Cherkasy region southeast of Kyiv.

Ukraine’s top diplomat said on Saturday that the day’s attacks were proof that Ukraine needed new Western-reinforced air defense systems “without a minute of delay.”

“Air defense saves lives,” Dmytro Kuleba wrote on Twitter.

Kyrylo Tymoshenko, the deputy head of Ukraine’s presidential office, said on Telegram on Saturday that almost 1.4 million households lost power as a result of the strikes. He said some 672,000 homes in the western Khmelnytskyi region were affected, while a further 242,000 suffered outages in the central Cherkasy province.

Most of the western city of Khmelnytskyi, which straddles the Bug river and was home to some 275,000 people before the war, was left with no electricity, shortly after local media reported several loud explosions.

The city council urged local residents to store water, “in case it’s also gone within an hour,” in a social media post on Saturday.

The mayor of Lutsk, a city of 215,000 in Ukraine’s far west, made a similar appeal on Telegram on Saturday. Power in Lutsk had been partially knocked out after Russian missiles slammed into local energy facilities, Ihor Polishchuk said. He later added that a civilian had suffered burns as a shockwave from the strike hit his house, and that one power station had been damaged beyond repair.

The central city of Uman, a key pilgrimage center for Hasidic Jews which counted some 100,000 residents before the war, was also plunged into darkness after a rocket hit a nearby power station, regional authorities said on Telegram.

Ukraine’s state energy company responded to the strikes by announcing that rolling blackouts would be imposed in Kyiv and 10 Ukrainian regions in order to stabilize the situation.

In a Facebook post on Saturday, Ukrenergo accused Russia of attacking “energy facilities within the principal networks of the western regions of Ukraine.” It claimed that the scale of destruction has been comparable to the fallout from Moscow’s first coordinated attack on the Ukrainian energy grid, Oct. 10-12.

Both Ukrenergo and officials in Kyiv have been urging Ukrainians to conserve energy. Earlier this week, President Volodymyr Zelenskyy called on consumers to curb their power use between 7 a.m. and 11 a.m. daily, and avoid using energy-guzzling appliances such as electric heaters.

Over the past two weeks, Moscow has increased its attacks on key civilian infrastructure across Ukraine. About 40% of the country’s electric power system has been severely damaged, officials said. Zelenskyy said earlier in the week that 30% of Ukraine’s power stations have been destroyed since Russia launched the first wave of targeted strikes on Oct. 10.

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Kozlowska reported from London.