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Late on Thursday evening, President Volodymyr Zelenskyj decreed general mobilization. This puts conscripts and all reservists from across the country on standby.
The head of state reported 137 dead in fighting after the invasion of Russia.
The United Nations refugee agency UNHCR estimates that around 100,000 people have left their homes in Ukraine so far.
In a conversation with the Austrian Prime Minister Karl Nehammer, the President of Ukraine had previously stated that he did not know how long his country would exist, because he would still be in office or alive.
In Kiev and other cities, Ukrainians spend the night in air raid shelters.
US President Joe Biden declared: "Putin is the aggressor" – and he must bear the consequences of his actions.
Russian troops have taken over the region of the former Chernobyl nuclear power plant, where the "worst possible accident" (GAU) happened in 1986 and covered all of Europe with a radioactive cloud.
After the Russian troops invaded, President Volodymyr Zelenskyy called on all Ukrainians to "make their contribution to the defense of the country". Anyone with military training and experience should report to the Department of Defense.
Russia attacked Ukraine "insidiously and viciously" just as fascist Germany attacked Ukraine in World War II. "Russia is on the side of evil," the president said.
In the early morning of February 24, 2021, Kremlin chief Vladimir Putin officially ordered a Russian military mission abroad in the Luhansk and Donetsk regions in the conflict with Ukraine.