A baby aged just 22 days, her 12-year-old brother and their parents were among seven people killed by Russian shells in southern Ukraine on Sunday.
Bombs hit their family home in the village of Shyroka Balka in Kherson, Interior Minister Igor Klymenko said.
The dead also included another village resident and two men in neighbouring Stanislav.
"Terrorists must be stopped. They must be stopped by force," said Mr Klymenko. "They don't understand anything else."
The minister shared photographs of the aftermath of the attack on Shyroka Balka, showing black columns of smoke rising from buildings, and the digitally obscured bodies of some of the dead.
Thirteen others were injured in the shelling, he added.
Ukraine President Volodymyr Zelensky used his daily address to the nation to condemn the "brutal" attack in Shyrokа Balka.
"Five people were killed," he said. "Among them was a baby girl, only 22 days old. Her brother, just 12 years old. The mother Olesia... only 39, also perished."
He added there had been 17 reports of Russian shelling in Kherson alone, and many more beyond.
"There is no day when Russian evil does not receive our entirely just response," he said.
"We will not leave any of Russia's crimes unanswered."
Kherson was one of four regions in Ukraine that Russian President Vladimir Putin claimed to have annexed last year.
Ukraine's military reclaimed the western part of the region in November. Russian troops have continued to shell the area from across the Dnipro river.
The shelling came a day after Moscow accused Kyiv of "terrorism" for what it said was an attempted missile strike on the Crimean Bridge linking the peninsula to Russia.
Ukraine has not confirmed the attack, although Mr Zelensky has previously said the bridge is used as a military supply route and is a legitimate target.
Crimea has been under Moscow's control since Russian forces annexed the peninsula in 2014 - a move condemned internationally.
In another development, Moscow said it had fired warning shots at a cargo ship in the southwestern Black Sea to halt it for an inspection as it made its way to the Ukrainian port of Izmail on the Danube river.
The Russian claim has not been independently verified. If confirmed, it would be the first time Russia has fired on merchant shipping beyond Ukraine since exiting a landmark UN-brokered grain deal last month.
Russia said that its Vasily Bykov patrol ship had fired automatic weapons toward the Palau-flagged Sukru Okan when it refused to halt, then boarded for an inspection.
Meanwhile, an aide to the exiled Ukrainian mayor of Mariupol reported that several Ukrainian civilians were killed as Russian soldiers fought among themselves on Sunday.
Two teenage girls, four young men and a woman were among the dead in the "shoot-out" in the village of Urzuf, Petro Andryshchenko said in a Telegram post.
He said the gun battle followed an argument between Chechen troops and personnel from the local commandant's office.
Mariupol, a major port on the Sea of Azov, was captured by Russia after months of fierce fighting last year.