Ukraine President Volodymyr Zelenskyy has called a Russian airstrike on a shopping mall that left at least 18 dead "one of the most daring terrorist attacks in European history." 

Rescuers were still searching for survivors Tuesday amongst the rubble in the city of Kremenchuk, where the building – which Zelenskyy said had "more than a thousand civilians" inside – was hit Monday afternoon. 

In his nightly address, the Ukraininan president said that Russian forces intentionally targeted the shopping center in "one of the most daring terrorist attacks in European history," and denounced Russia as "the largest terrorist organization in the world." 

Casualty figures continue to rise as rescuers sift through the smoldering debris. Regional Governor Dmytro Lunin said at least 18 people were killed, and 59 others sought medical assistance. The region declared a day of mourning Tuesday for the victims of the attack. 

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Ukraine Kremenchuk Mall Russia airstrike

Ukrainian State Emergency Service firefighters work to take away debris at a shopping center burned after a rocket attack in Kremenchuk, Ukraine, on Tuesday, June 28.

"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," emergency services official Volodymyr Hychkan said. 

Ukraine’s Prosecutor General, Iryna Venediktova — who is leading investigations into possible war crimes — said the missile attack was one of Russia’s "crimes against humanity," and noted that the Russian military has been "systematically shelling civilian infrastructure with the aim to scare people, to kill people, to bring terror to our cities and villages." 

Firefighters assist at Ukraine Kremenchuk mall disaster

Ukrainian State Emergency Service firefighters are seen on Tuesday, June 28, working in the rubble of the mall.

Venediktova emphasized the need for Ukrainians across the entire country to remain alert, adding that they should expect a similar strike "every minute." 

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

Fire at Kremenchuk mall

Russian airstrikes hit a shopping mall in Kremenchuk on Monday, according to Ukrainian President Volodymyr Zelenskyy. (Ukrainian President Volodymyr Zelenskyy Telegram)

G7 leaders also condemned the violence, and issued a joint statement calling the airstrike "abominable" and noting that "indiscriminate attacks on innocent civilians constitute a war crime." 

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"Russian President Putin and those responsible will be held to account," the statement added. 

Russia’s Defense Ministry, meanwhile, has claimed its forces launched missiles at a storage depot for Western weapons in Kremenchuk and stated that the ensuing detonation of ammunition there sparked the massive fire and destruction at the mall, Reuters has reported, citing state media. 

The Associated Press contributed to this report.