Russian drone and missile strikes hit Kharkiv and Sumy shortly after Ukraine announced a ceasefire, damaging homes and killing a security guard at a kindergarten.
Ukrainian officials say the attacks show Moscow is not serious about ending the war.
Russia has proposed a separate two-day truce around its May 9 Victory Day parade, warning Kyiv not to interfere.
President Volodymyr Zelenskyy and residents expressed skepticism about any lasting ceasefire.