Ukrainian President Volodymyr Zelenskiy said the Russian forces that attacked the Ukrainian Black Sea port city of Odesa with Iskander missiles and drones on March 15 would receive a "fair response" from Kyiv's forces.
The air strike killed 20 people and injured more than 70, Ukraine's State Emergency Services said.
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Two Russian Iskander-M missiles, fired from Russian occupied Crimea, struck a residential area in Odesa, said Oleh Kiper, governor of the region. Several of the dead were medics and rescuers who were killed by a second missile after they rushed to the scene to treat people hurt in the initial strike, Kiper added.
Zelenskiy denounced the attack as "heinous" and referred to the Russian forces that carried it out as "scum."
Russia has stepped up its strikes on the southern city in recent weeks, launching drones or missiles almost every day this month. The March 15 attack was one of the deadliest in weeks.
"Russia continues to terrorize Odesa," said Ukrainian Prosecutor-General Andriy Kostin on Facebook, noting the local residents, doctors, and emergency responders killed after they rushed to the scene of the first missile strike. Ten people suffered serious injuries, he added.
March 16 has been declared a day of mourning, and a criminal investigation has been launched.
Zelenskiy met with military commanders, including Defense Minister Rustem Umerov, saying afterward on Telegram that the officials identified the enemy's "most vulnerable places," adding that the greater the price Russia must pay for its aggression, "the closer the just end of this war will be."
He also called for the production of more high-tech drones with longer ranges for future operations.
A separate attack on Ukraine's Vinnytsya region killed at least two people, while Russia's border region of Belgorod and a refinery in the western region of Kaluga were reportedly targeted again by drones and missiles.
A Russian drone struck a residential building in Vinnytsya, the capital of the region with the same name in western Ukraine, killing one person and injuring four, Serhiy Borzov, the regional governor, said on Telegram. He later said a second victim, a woman, died in the hospital.
Ukrainian First Responders Killed In Russian Missile Strike In Odesa
The Ukrainian military said separately that Russia launched 27 Shahed-type drones and eight missiles at seven Ukrainian regions.
"All 27 Shahed attack drones were shot down above the Kirovohrad, Mykolayiv, Kharkiv, Kherson, Khmelnytskiy, Vinnytsya, and Kyiv regions,” the military said in a statement, adding that many of the drones had been heading toward the capital.
The military did not specify whether missiles were also shot down.
In Russia, where three days of voting got under way in a presidential election featuring incumbent Vladimir Putin whose outcome is not in doubt, officials reported more alleged attacks by Ukrainian drones and missiles on the border region of Belgorod.
In the regional capital of Belgorod, which has been targeted by cross-border attacks for several days in a row, fresh missile and drone strikes wounded two people, damaged several residential buildings, and disrupted the voting, regional Governor Vyacheslav Gladkov said on Telegram.
A video circulating on social media purportedly shows a van on a Belgorod street being struck by a projectile and exploding. It was not immediately clear whether there were people in the van.
Russia's Defense Ministry said its air-defense systems had downed all drones and missiles allegedly launched by Ukraine on Belgorod.
On March 14, two people were reportedly killed in Belgorod in explosions on the roads that appeared to have been caused by projectiles. There were also unconfirmed reports of repeated cross-border incursions by groups of Russians who are fighting on Ukraine's side.
Separately, Baza Telegram channel, which is linked to Russian security services, reported a fire at the Pervy Zavod refinery in Kaluga that it said was caused by debris from one of four drones shot down by Russian air-defense systems. It said the fire was "quickly localized."
However, a report on social media, accompanied by a video showing a purported blast at an industrial outlet resembling a refinery, said three out of four drones actually struck the Pervy Zavod.
A Ukrainian intelligence source told Reuters that the drone attack on the Kaluga refinery caused damage and was conducted by Ukraine's HUR military intelligence service.
The source, who spoke on condition of anonymity, said Ukraine was checking the extent of the damage. The statement could not be independently verified.
Dozens of Ukrainian drones struck energy infrastructure in several Russian regions in recent days, including oil refineries in Ryazan, Nizhny Novgorod, and the Leningrad region.