Russian shelling killed seven people, including a 23-day-old infant, and wounded 20 in Ukraine's southern region of Kherson on Sunday, prompting local officials to declare Monday a day of mourning.

Kyiv reclaimed part of Kherson from Russian occupation last November but Kremlin troops have continued shelling the regional capital and areas around it from across the Dnipro River.

A couple, their 23-day-old child and another man were killed in the village of Shyroka Balka, Interior Minister Ihor Klymenko said. The couple's 12-year-old son was critically wounded and died in hospital, he added.

"The terrorists will never willingly stop killing civilians," Klymenko wrote in a Telegram post. "The terrorists must be stopped. With force. They don't understand anything else."

Two people, including the pastor of a church, were killed in the neighboring village of Stanislav, according to Governor Oleksandr Prokudin.

Three people each in Kherson city and the town of Beryslav were wounded, according to the interior ministry, and casualties were also reported in four other settlements across the region.

"Today the Kherson region shuddered from terrible news. Kherson, Veletenske, Zolota Balka, Stanislav, Komyshany, Shyroka Balka..." Prokudin wrote on Telegram, listing the settlements hit in Sunday's attacks.

Ukraine's military launched a counteroffensive in June to reclaim Russian-occupied territory across the southeast but has not made any significant attempts to cross the Dnipro to reach the other side of the Kherson region.