Smoke rises from the Azovstal steel mill in Mariupol, eastern Ukraine, on Wednesday. AP

Heavy fighting also raged on Wednesday at the Azovstal steel mill in Mariupol that represented the last stronghold of Ukrainian resistance in the ruined southern port city, according to the mayor. A Russian official denied that Moscow's troops were storming the plant, but the commander of the main Ukrainian military unit inside said Russian soldiers had pushed into the mill's territory.

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The Russian military said it used sea- and air-launched missiles to destroy electric power facilities at five railway stations across Ukraine. Artillery and aircraft also struck troop strongholds and fuel and ammunition depots.

Ukrainian Foreign Minister Dmytro Kuleba accused Russia of "resorting to the missile terrorism tactics in order to spread fear across Ukraine.”

Rubble from the damaged Donetsk Academic Regional Drama Theatre sits after the bombing in Mariupol. AP

Air raid sirens sounded in cities across the country on Wednesday night, and attacks were reported near Kyiv, the capital; in Cherkasy and Dnipro in central Ukraine; and in Zaporizhzhia in the southeast. In Dnipro, authorities said a rail facility was hit. Videos on social media suggested a bridge there was attacked.

There was no immediate word on casualties or the extent of the damage.

Responding to the strikes in his nightly video address, Ukrainian President Volodymyr Zelensky said: "All of these crimes will be answered, legally and quite practically - on the battlefield.”

The flurry of attacks comes as Russia prepares to celebrate Victory Day on May 9, marking the Soviet Union’s defeat of Nazi Germany. The world is watching for whether Russian President Vladimir Putin will use the occasion to declare a victory in Ukraine or expand what he calls the "special military operation.”

This satellite image shows smoke rising at the Azovstal steelworks in Mariupol, Ukraine, on Wednesday. AP

A declaration of all-out war would allow Putin to introduce martial law and mobilize reservists to make up for significant troop losses.

Kremlin spokesman Dmitry Peskov dismissed the speculation as "nonsense.”

In Mariupol, Mayor Vadym Boychenko said that Russian forces were targeting the already shattered Azovstal plant with heavy artillery, tanks, aircraft, warships and "heavy bombs that pierce concrete 3 to 5 meters thick.”

"Our brave guys are defending this fortress, but it is very difficult,” he said.

Ukrainian fighters said Tuesday that Russian forces had begun storming the plant. But the Kremlin denied it. "There is no assault," Peskov said.

A cat walks next to a tank of Donetsk People's Republic militia in Mariupol, eastern Ukraine, on Wednesday. AP

Denys Prokopenko, commander of the Ukrainian Azov regiment that's defending the plant, said Russian forces got into the plant's territory.

Prokopenko said in a video that the incursions continued for a second day, "and there are heavy, bloody battles.”

"The situation is extremely difficult, but in spite of everything, we continue to carry out the order to hold the defense,” he added.

His wife, Kateryna Prokopenko, told the media: "We don’t want them to die. They won’t surrender. They are waiting for the bravest countries to evacuate them."

Associated Press