Ukrainian President Volodymyr Zelensky on Monday warned global business leaders that sanctions on Russia must be increased to discourage other countries from employing “brute force” to achieve their goals.

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Zelensky spoke to the World Economic Forum in Davos via video link as the Ukrainian military claimed to have repulsed a Russian assault on Sievierodonetsk, an eastern city that has become the main target of a Russian offensive following the surrender of Mariupol, Ukraine’s southern port city, last week.

On Monday, Zelensky revealed Ukraine’s biggest military losses in a single attack since the war began, saying 87 people were killed when Russian forces struck a barracks holding troops at a training station in the north.

Previously, Kyiv claimed that eight individuals were killed in the May 17 strike on the Desna barracks.

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A court in Kyiv sentenced a young Russian tank commander to life in prison for killing an unarmed civilian in the first of what may be many war crimes cases stemming from Russia’s Feb. 24 invasion.

According to Ukraine Prosecutor-General Iryna Venediktova, around 13,000 cases of Russian alleged war crimes are being examined.

Russia has denied targeting people or engaging in war crimes while conducting a “special military operation” in Ukraine.

With the crisis entering its fourth month, Zelensky encouraged countries to increase pressure on Moscow, accusing them of not exhausting sanctions.

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“The sanctions should be maximum, so that Russia – and every other potential aggressor who wants to wage a brutal war against its neighbour – clearly knows the immediate consequences of their actions,” he stated during the Davos summit.

He called for an oil embargo, the closure of all Russian banks, and the cessation of all trade. Foreign companies should leave Russia, and the Russian IT industry should be cut off from the West, he stated.

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The United States, the European Union, and other countries have already slapped wide sanctions on Russia, and Starbucks Corp became the latest Western company to declare its withdrawal from the nation on Monday. The Seattle-based coffee company operates 130 locations in Russia. Its choice is comparable to one made by McDonald’s. On Monday, the fast-food chain’s iconic “Golden Arches” were demolished near Moscow.