Russian-installed authorities in the occupied city of Kherson on Saturday urged residents to leave immediately in the face of a looming counteroffensive by Ukraine’s armed forces whose aim was to recapture the southern city.

“Due to the tense situation at the front, the increased danger of massive shelling of the city and the threat of terrorist attacks, all civilians must immediately leave the city,” a statement on the Russian administration’s Telegram channel said Saturday.

Urging people to board boats across the Dnieper River, Russia also said in the statement that all departments and ministries of the Kremlin-installed administration should also leave the southern city, which has been in the hands of Russian forces since they invaded Ukraine in February.

Ukrainian forces bombarded Russian positions and targeted supply routes across the province on Friday, inching closer to a full assault on the only provincial capital that has remained in Russian hands throughout the war.

The Kakhovka Hydroelectric Power Plant (Olga Maltseva / AFP via Getty Images file)© Olga Maltseva

The order came after Ukrainian President Volodymyr Zelenskyy said Russian forces had planted explosives inside the huge Nova Kakhovka dam on the Dnieper River, which holds back an enormous reservoir.

In a late-night television address he said Moscow was planning to blow up the dam and that “would mean a large-scale disaster.”

Russia has accused Kyiv of firing rockets at the dam. Neither side produced evidence to back up their allegations.

Zelenskyy’s comments came before more than 1 million people woke up without power Saturday, after a wave of Russian strikes pounded critical infrastructure in several cities across the country, Kyrylo Tymoshenko, a deputy head of the Ukrainian president’s office, said in a statement.

Infrastructure in the southern city of Odesa had also been hit, he said.

NBC News could not independently verify these claims, but officials in the western cities of Lviv, Khmelnytskiy, Volyn and Rivne also reported attacks.

“As a result of the strikes, there is no power supply in part of the Rivne district,” Vitaly Koval, the governor of Rivne, said on his Telegram channel, adding that electrical substations had been damaged. He said the attacks produced no casualties.

His comments were echoed by Ihor Polishchuk, the mayor of Lutsk, who said in a post on his Facebook page that part of the city had lost its electricity supply.

Firefighters work to put out a fire in residential building after a© Provided by NBC News

Elsewhere, Iran‘s Foreign Ministry said it condemned a call by France, Germany and Britain for the United Nations to investigate allegations that Russia has used Iranian-made drones to attack Ukraine, according to the Iranian state-run news agency, IRNA.

In a letter signed by their U.N. envoys, the three European countries backed Ukraine’s call on Monday for a U.N. investigation, arguing the use of Shahed-136 attack drones, known as kamikaze drones, breached the terms of the 2015 Iran nuclear deal.

The White House said Thursday it had evidence that Iran had sent military officers to Russian-occupied territories in Ukraine to help Moscow launch drone attacks on targets across the country.

Iran sent trainers and technical support to enable Russian forces to use Iranian-made drones “with better lethality,” John Kirby, White House National Security Council spokesperson, told reporters.

“We assess that Iranian military personnel were on the ground in Crimea and assisted Russia in these operations,” he said.