Buildings in the southern Ukrainian port city of Odessa lay in ruins as firefighters battled blazes into the early hours on Tuesday, a day after Russian forces pounded the port with missiles and President Vladimir Putin led defiant celebrations marking the Soviet's victory over Nazi Germany in World War II.

While Putin was silent about plans for any escalation, he exhorted Russians to battle and repeated his assertions that they were again fighting Nazis. His forces continued to destroy the infrastructure of the Azovstal steel plant in Mariupol where the last Ukrainian troops are holding out.

"You are fighting for the Motherland, for its future, so that no one forgets the lessons of World War II. So that there is no place in the world for executioners, castigators and Nazis," Putin said.

Ukraine's President Volodymyr Zelenskyy, in his own speech on Monday, promised Ukrainians would triumph.

"On the Day of Victory over Nazism, we are fighting for a new victory. The road to it is difficult, but we have no doubt that we will win," said Zelenskyy.

In Odessa, the major Black Sea port for exporting agricultural products, one person was killed and five people were injured when seven missiles hit a shopping center and a depot, Ukraine's armed forces said on Facebook.

Ukrainian officials found the bodies of 44 civilians in the rubble of a building in the northeast that was destroyed weeks ago.

Meanwhile, a Ukrainian official said that at least 100 civilians remain trapped at a steel mill in the besieged city of Mariupol, where Ukrainian fighters are making a last stand.

"This is another horrible war crime of the Russian occupiers against the civilian population!" said Oleh Synehubov, the head of the regional administration, in a social media message announcing the deaths.

Ukraine and its allies have intensified efforts on how to unblock ports or provide alternate routes for exporting its significant crops of grain, wheat and corn.

European Council President Charles Michel visited Odessa on Monday, and his meeting with Ukrainian Prime Minister Denys Shmyhal was interrupted by the missile attack.

Their talks continued in a bomb shelter, according to Shmyhal's official Twitter account.

Air raid sirens could be heard across several regions of Ukraine early on Tuesday including Luhansk, Kharkiv and Dnipro.

Serhiy Haidai, the governor of Luhansk, said the region was attacked 22 times in the 24 hours to early Tuesday.

"During the day on May 9, the Russians fired en masse on all possible routes out of the region," he said.

In the town of Bogodukhov, northwest of Kharkiv, four people were killed and several homes were destroyed in Russian attacks on Monday, local media quoted Kharkiv officials as saying.

The Ukrainian Defense Ministry said Russian forces backed by tanks and artillery were conducting "storming operations" at Mariupol's Azovstal plant, where hundreds of Ukrainian defenders have held out through months of siege.

Mariupol lies between the Crimean Peninsula, seized by Moscow in 2014, and parts of eastern Ukraine under the control of Russia-backed separatists. Capturing the city would allow Moscow to link the two areas.

'Revisionist disinformation'

More than 5.5 million Ukrainians have fled their country since Russia's invasion on Feb. 24, according to the United Nations, which has called it Europe's fastest-growing refugee crisis since World War II.

Moscow's gains from the invasion, however, have been slow at best and it has little to show for it beyond a strip of territory in the south and marginal gains in the east.

U.S. President Joe Biden said he was worried Putin "doesn't have a way out right now, and I'm trying to figure out what we do about that."

Sources say U.S. Democratic lawmakers have agreed on a $40 billion aid proposal for Ukraine, including a massive new weapons package.

The White House had earlier described Putin's remarks during his Victory Day speech as "revisionist history that took the form of disinformation."

The Soviet victory in World War II has acquired almost religious status in Russia under Putin, who has invoked the memory of the "Great Patriotic War" throughout what he calls a "special military operation" in Ukraine.

Western countries consider that a false analogy to justify what they see as unprovoked aggression.

"There can be no victory day, only dishonor and surely defeat in Ukraine," said British Defence Secretary Ben Wallace.