Air raid sirens blared across most Ukrainian cities on Saturday morning urging people to seek shelters, local media reported, after President Volodymyr Zelensky said the war had reached a "strategic turning point".
Russian forces appeared to be regrouping, possibly for a fresh offensive that could target the capital Kyiv, Ukraine's military and Britain's defense ministry said.
Efforts to isolate Russia economically stepped up, with the United States imposing new sanctions on senior Kremlin officials and Russian oligarchs and the European Union set to strip Russia of its privileged trade status on Saturday.
With the Russian assault in its third week, Zelensky, who has rallied his people with a series of addresses from the capital Kyiv, said Ukraine had "already reached a strategic turning point".
"It is impossible to say how many days we still have (ahead of us) to free Ukrainian land. But we can say we will do it," he said. "We are already moving towards our goal, our victory."