President Joe Biden condemned Russia’s attack on Ukraine as “unprovoked and unjustified” and promised to hold it accountable as Moscow launched what appeared to be a long-anticipated invasion of its neighbour.

       Mr Biden’s comments followed a declaration by Russian president Vladimir Putin of a “special military operation” in Ukraine, which would aim for the “demilitarisation” of the country. Soon after Mr Putin’s announcement, in a televised speech broadcast just before 6am local time, explosions were reported in several Ukrainian cities, including the capital Kiev.

       Mr Biden said the Russian president “has chosen a premeditated war that will bring a catastrophic loss of life and human suffering”.

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       “Russia alone is responsible for the death and destruction this attack will bring, and the United States and its Allies and partners will respond in a united and decisive way,” he added in the statement.

       “The world will hold Russia accountable,” Mr Biden continued.

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       Shortly after the strikes began, Ukraine’s foreign minister Dmytro Kuleba said that Putin had “just launched a full-scale invasion of Ukraine.”

       “Peaceful Ukrainian cities are under strikes. This is a war of aggression. Ukraine will defend itself and will win. The world can and must stop Putin. The time to act is now,” he wrote on Twitter.

       Mr Putin said earlier that Russia has been left with no choice but to defend itself against what he said were threats emanating from modern Ukraine.

       "Russia cannot feel safe, develop, and exist with a constant threat emanating from the territory of modern Ukraine," said Putin.

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       Putin said Russia would respond instantly if any external force tried to interfere and that Moscow would try to de-militarise and “de-Nazify” Ukraine.

       —With Reuters