Russian bombs tore into Ukrainian cities on Tuesday afternoon and evening, killing more than 20 people and wounding dozens of others.

The deadly strikes drew a furious response from President Volodymyr Zelensky of Ukraine, who said they showed the cynicism behind Russia’s announcement of a cease-fire timed to Moscow’s Victory Day celebrations on May 9.

Mr. Zelensky had challenged the announcement of the truce by President Vladimir V. Putin of Russia by proposing instead an open-ended cease-fire beginning at midnight on Tuesday. He said that Ukraine sought a lasting cease-fire, not just a break to protect a parade in Moscow.

At least 12 people were killed and 37 others wounded in the southern city of Zaporizhzhia as the daytime Russian strikes got underway on Tuesday afternoon, according to Ukraine’s emergency services. The toll in Zaporizhzhia was one of the highest from a single attack so far this year. Separate strikes also killed at least four people in the city of Dnipro and five in the center of Kramatorsk, according to the Ukrainian authorities.

Images posted on social media of the aftermath in Kramatorsk showed bodies in the street, with flames and thick black smoke.

Mr. Zelensky said the “absolutely cynical” strike in Zaporizhzhia had targeted civilian infrastructure, and he accused Russian forces of showing “no restraint in destroying human life.”

“We need silence from such strikes and all others like them every single day, not just for a few hours somewhere out there for ‘celebrations,’” he wrote in a scathing post on social media that shared images of the destruction.

Air-raid warnings sounded as rescuers dug through the rubble and firefighters worked to extinguish burning vehicles and businesses. Residential buildings, a car repair shop and a carwash sustained damage, according to Ivan Fedorov, the head of the regional military administration. Mr. Fedorov said Wednesday would be an official day of mourning.

Large-scale daytime attacks are a less common occurrence in Ukraine, where most nights are filled with wailing air-raid sirens warning of incoming Russian drones and missiles. The wee hours of Tuesday were no different, when at least four Ukrainians were killed by a Russian strike on a gas production facility in the Poltava region on Monday night into early Tuesday.

Ukraine has conducted several strikes on energy-related facilities deep inside Russia in recent weeks, part of an expansion of its long-range strikes. Mr. Putin’s announcement of the Saturday cease-fire and the Kremlin’s decision to significantly scale back its Victory Day Parade were seen as an acknowledgment of the growing threat posed by Ukrainian drones.

That risk was underscored when a drone slammed into a Moscow high-rise on Monday. While Ukraine did not claim responsibility for that attack, Mr. Zelensky said Russia’s decision to downsize the parade showed its weakness and “fear drones may buzz over Red Square.”

On Tuesday, he highlighted Ukraine’s deep-strike campaign in announcing that Ukrainian missiles had traveled more than 1,500 kilometers (about 930 miles) to strike targets in the Cheboksary region of Russia. The long-range attacks, he said, were an “entirely just response to Russian strikes.”

A few hours later, explosions cut through Zaporizhzhia’s sunny afternoon.