Russia announced a ceasefire for May 8-9, dates when it commemorates the Soviet Union victory over Nazi Germany in World War II and holds a military parade.
Ukraine, in response, announced a proposal for an open-ended ceasefire starting at midnight on Wednesday, urging Russia to reciprocate.
President Volodymyr Zelenskiy said it was not an option for Russia to halt strikes for one day for its military parade while having heavily pounded Ukraine.
At least 12 people were killed in the city of Zaporizhzhia, emergency services said on the Telegram app.
According to the regional governor Ivan Fedorov, at least 16 more were injured.
Residential buildings, a car repair service and a car wash were damaged in the attack, he said.
The attack also sparked fires at a shop and an unidentified enterprise, he added.
Images from the site that he shared showed a heavily damaged building with billowing flames and smoke.
Cars are seen burning as first responders help bloodied people leave the site.
Three aerial bombs dropped on the eastern frontline city of Kramatorsk killed five other people, Zelenskiy said on Telegram.
Five people were injured, he added, warning that the death toll might rise.
A Russian overnight strike on the gas production facilities in the Poltava region killed five, Ukrainian officials said.
Ukraine's government made clear on Tuesday that it was prepared to extend indefinitely a ceasefire due to go into effect at midnight.
"If the ceasefire announced by the President (Volodymyr Zelenskiy) is reciprocated, we will continue to observe it. And this will give us at least a small glimmer of hope for achieving a lasting peace," presidential office head Kyrylo Budanov posted on social networks.
"The next move is Russia's," he said.
"We are closely monitoring every move by the enemy and are prepared for any possible developments," he added.
In Russia, a Ukrainian drone attack on the Chuvashia region killed two on Tuesday, the Russian state news agency reported.
Russia's vast Kirishinefteorgsintez (Kirishi) oil refinery halted processing on Tuesday following Ukrainian drone attacks which damaged the plant's units and caused a fire, two industry sources said.
The sources, who spoke to Reuters on condition of anonymity due to the sensitivity of the situation, said that three of the four crude distillation units of the refinery were damaged in the drone attack.
It is hard to estimate the time required for repairs of the damaged units, the sources said, adding that several secondary units were also damaged.
Leningrad's region governor Alexander Drozdenko said early on Tuesday there was a fire at industrial zone in Kirishi.
with DPA
