Russia launched its invasion by land, air and sea on Thursday (Feb 24) following a declaration of war by President Vladimir Putin.
An estimated 100,000 people have fled as explosions and gunfire rocked major cities.
Ukrainian President Volodymyr Zelenskyy said that 137 Ukrainians, both military personnel and civilians, were killed in the first day.
US and Ukrainian officials say Russia aims to capture Kyiv and topple the government. Russia on Thursday seized the Chernobyl former nuclear power plant north of Kyiv, along the shortest route to the capital from Belarus, where Moscow has staged troops.
Zelenskyy vowed on Friday to stay in Kyiv, despite Russia identifying him as "target number one".