Russia attacked Odesa on April 29 with an Iskander missile armed with a cluster munition warhead, Prosecutor General Andrii Kostin said on April 30.
Russian forces attacked the southern port city late on April 29, killing at least five people and injuring around 30, including children.
"This (cluster munition) is an indiscriminate weapon, the use of which can lead to significant casualties among the civilian population," the Prosecutor General's Office said on Telegram, citing Kostin.
"The investigators have a reason to believe that the decision to use such a weapon was taken by the Russian military officers deliberately to kill as many Ukrainian civilians as possible."
According to the prosecutors, fragments of the missile were uncovered within a radius of 1.5 kilometers from the site of impact.
"The investigation is ongoing. We will find and punish those who issue criminal orders to attack peaceful Ukrainian cities," Kostin said.
Ukrainian officials have repeatedly accused Russia of using cluster munitions to target civilian areas. These weapons "spray" small bomblets across a wide area, with some of them detonating long after the attack, posing a continued danger to the local population.
In a post on social media, President Volodymyr Zelensky said more support was needed from Ukraine's allies to stop "Russia's regular missile attacks, as well as the occupier's efforts to destroy as many Ukrainian positions as possible."
"And Russia's offensive plans can be thwarted," he said, adding: "For this, Ukrainian strength must be backed up by sufficient support from partners – 'Patriots' that need to be in Ukraine now, the 155-mm caliber (artillery ammunition)... and weapons with sufficient range to destroy Russian logistics."
Odesa Oblast and other southern regions of Ukraine are regular targets of Russian missile and drone attacks.