Russia has been widely condemned after bombarding cities across Ukraine, including launching missile strikes on the centre of Kyiv for the first time.
The US said “brutal” attacks had hit non-military targets and promised ongoing military aid, including advanced air defence systems.
United Nations chief Antonio Guterres said he was “deeply shocked”.
Vladimir Putin said the attacks were retaliation for Saturday’s explosion on a key bridge linking Russia to Crimea.
The deadly violence across Ukraine included strikes on the cities of Lviv, Kharkiv, Dnipro and Zaporizhzhia.
At least 14 people were killed and scores more were injured, officials said.
In Kyiv the areas hit included the Taras Shevchenko park, a university building, and a children’s playground.
Antonio Guterres described the strikes as “another unacceptable escalation of the war” for which civilians were paying the highest price.
The EU said a war crime had been committed, while European Commission president Ursula von der Leyen said Russia stood for terror and brutality.
US President Joe Biden was one of many foreign leaders to speak with President Volodymyr Zelensky, and he “pledged to continue providing Ukraine with the support needed to defend itself, including advanced air defence systems”, the White House said.
Mr Biden said the attacks demonstrated “the utter brutality” of Putin’s “illegal war”.
China and India, which have not condemned the war, called for a de-escalation. (BBC)