Firefighters work to extinguish a fire at a shopping center burned after a rocket attack in Kremenchuk, Ukraine, on Monday. Ukrainian State Emergency Service via Associated Press

KREMENCHUK, Ukraine — Russian long-range bombers fired a missile that struck a crowded shopping mall in Ukraine’s central city of Kremenchuk on Monday, raising fears of what President Volodymyr Zelensky called an “unimaginable” number of victims in “one of the most daring terrorist attacks in European history.”

Zelenskky said more than 1,000 civilians were inside the mall, with many managing to escape. Giant plumes of black smoke, dust and orange flames emanated from the wreckage, with emergency crews rushing in to search broken metal and concrete for victims and put out fires. Onlookers watched in distress.

The casualty figures were difficult to determine as rescuers searched the smoldering rubble. The regional governor, Dmytro Lunin, said at least 15 people were dead and more than 40 wounded.

Soldiers worked into the night to lug sheets of twisted metal and broken concrete, as one drilled into what remained of the shopping center’s roof. Drones whirred above, clouds of dark smoke still emanating from the ruins several hours after the fire had been put out.

Multiple deaths and injuries resulted from a Russian rocket attack on a crowded shopping center in Kremenchuk, Ukraine, on Monday. Ukrainian State Emergency Service via Associated Press

“We are working to dismantle the construction so that it is possible to get machinery in there since the metal elements are very heavy and big, and disassembling them by hand is impossible,” said Volodymyr Hychkan, an emergency services official.

At Ukraine’s request, the U.N. Security Council scheduled an emergency meeting in New York on Tuesday to discuss the attack.

The missile strike unfolded as Western leaders pledged continued support for Ukraine, and the world’s major economies prepared new sanctions against Russia, including a price cap on oil and higher tariffs on goods. Meanwhile, the U.S. appeared ready to respond to Zelensky’s call for more air defense systems, and NATO planned to increase the size of its rapid-reaction forces nearly eightfold – to 300,000 troops.

Zelensky said the mall presented “no threat to the Russian army” and had “no strategic value.” He accused Russia of sabotaging “people’s attempts to live a normal life, which make the occupiers so angry.”

In his nightly address, he said it appeared Russian forces had intentionally targeted the shopping center and added, “Today’s Russian strike at a shopping mall in Kremenchuk is one of the most daring terrorist attacks in European history.”

Russian Tu-22M3 long-range bombers flying over Russia’s western Kursk region fired the missile that hit the shopping center, as well as another that hit a sports arena in Kremenchuk, according to Ukrainian officials.

A police officer and a paramedic give first aid to a woman wounded by the Russian shelling in city center in Sloviansk, Donetsk region, Ukraine, on Monday. Efrem Lukatsky/Associated Press

The Russian strike carried echoes of attacks earlier in the war that caused large numbers of civilian casualties – such as one in March on a Mariupol theater where many civilians had holed up, killing an estimated 600, and another in April on a train station in eastern Kramatorsk that left at least 59 people dead.

“Russia continues to take out its impotence on ordinary civilians. It is useless to hope for decency and humanity on its part,” Zelensky said.

Kremenchuk Mayor Vitaliy Maletskiy wrote on Facebook that the attack “hit a very crowded area, which is 100% certain not to have any links to the armed forces.”

The United Nations called the strike “deplorable,” stressing that civilian infrastructure “should never ever be targeted,” U.N. spokesman Stephane Dujarric said. Group of Seven leaders issued a statement late Monday condemning the attack and saying that “indiscriminate attacks on innocent civilians constitute a war crime. Russian President Putin and those responsible will be held to account.”

The attack happened as Russia was mounting an all-out assault on the last Ukrainian stronghold in eastern Ukraine’s Luhansk province, “pouring fire” on the city of Lysychansk from the ground and air, according to the local governor. At least eight people were killed and more than 20 wounded in Lysychansk when Russian rockets hit an area where a crowd gathered to obtain water from a tank, Luhansk Gov. Serhiy Haidai said.

The eastern barrage was part of Russian forces’ intensified offensive aimed at wresting the eastern Donbas region from Ukraine. Over the weekend, the Russian military and their local separatist allies forced Ukrainian government troops out of Lysychansk’s neighboring city, Sievierodonetsk.

To the west of Lysychansk on Monday, the mayor of the city of Sloviansk – potentially the next major battleground – said Russian forces fired cluster munitions, including one that hit a residential neighborhood. Authorities said the number of victims had yet to be confirmed. The Associated Press saw one fatality: A man’s body lay hunched over a car door frame, his blood pooling onto the ground from chest and head wounds. The blast blew out most windows in the surrounding apartment blocks and the cars parked below, littering the ground with broken glass.

“Everything is now destroyed,” said resident Valentina Vitkovska, in tears as she spoke about the blast. “We are the only people left living in this part of the building. There is no power. I can’t even call to tell others what had happened to us.”

Before Monday’s attacks, at least six civilians were killed and 31 others wounded as part of intense Russian shelling against various Ukrainian cities over the past 24 hours – including Kyiv and major cities in the country’s south and east, according to Zelensky’s office. Shelling on Monday in Kharkiv, Ukraine’s second-largest city, killed at least five people and wounded 15.

Russian forces continued to target the key southern Black Sea port of Odesa. A missile attack destroyed residential buildings and wounded six people, including a child, Ukrainian authorities said.

In Lysychansk, at least five high-rise buildings and the last road bridge were damaged over the past day, Haidai said. A crucial highway linking the city to government-held territory to the south was rendered impassable. The city’s prewar population of around 100,000 has dwindled to fewer than 10,000.

Analysts say that Lysychansk’s location high on the banks of the Siverskiy Donets River gives a major advantage to Ukrainian defenders.

“It’s a very hard nut to crack. The Russians could spend many months and much effort storming Lysychansk,” said military analyst Oleh Zhdanov.

Servicemen work at the scene at a residential building following explosions in Kyiv, Ukraine, on Sunday. Nariman El-Mofty/Associated Press

In other developments, in Germany’s Bavarian Alps, leaders of the G7 countries unveiled plans to seek new sanctions and pledged to continue supporting Ukraine “for as long as it takes.” In a joint statement Monday after they held a session by video link with Zelensky, the leaders underlined their “unwavering commitment to support the government and people of Ukraine in their courageous defense of their country’s sovereignty and territorial integrity.”

Elsewhere, Washington was expected to announce the purchase of an advanced surface-to-air missile system for Ukraine.

In Brussels, NATO Secretary-General Jens Stoltenberg announced plans to greatly expand the alliance’s rapid-reaction forces as part of its response to an “era of strategic competition.” The NATO response force currently has about 40,000 soldiers. NATO will agree to deliver further military support to Ukraine – including secure communication and anti-drone systems – when its leaders convene in Spain for a summit later this week, Stoltenberg said.

Britain’s defense ministry said Russia is likely to rely increasingly on reserve forces in the coming weeks. Analysts have said a call-up of reservists by Russia could vastly alter the balance in the war but could also come with negative political consequences for President Vladimir Putin’s government.