Russian missiles on Friday hit a medical clinic in the central Ukrainian city of Dnipro, killing at least two people, as Russia blamed Kyiv for dozens of strikes on its southern Belgorod region.
In Moscow, Russian Foreign Minister Sergei Lavrov discussed the Ukraine conflict with China's special envoy Li Hui, blaming Ukraine and Western countries for creating "serious obstacles" to resuming peace talks.
In Belgorod in southern Russia, the governor said the Ukrainian military was responsible for dozens of artillery, mortar and drone attacks across the region but reported no casualties.
Ukrainian President Volodymyr Zelensky posted a video of smoke billowing from roofless buildings with blown-out windows after the attack that authorities said had left 30 people injured including two boys aged three and six.
The head of the regional military administration Sergiy Lysak said that Russia struck a residential area with a medical and veterinary clinic and high-rise blocks.
Zelensky said that by hitting civilian medical facilities, "Russian terrorists once again confirm their status of fighters against everything humane and honest."
US Senator Lindsey Graham, on his third visit to Ukraine, condemned the attack as a war crime.
"There was a hospital bomb today. Just over 500 medical facilities have been hit by the Russians. A war crime was committed while I was here, just one of many war crimes," he said.
The Russian defence ministry said that its strikes on Ukraine had targeted arms depots and that all the assigned targets had been hit.
Ukrainian journalists posted video footage of rescuers helping people with blood on their faces escape from the clinic through corridors full of rubble.
The attack came after Russian forces earlier this week targeted Dnipro in a late night strike with 16 missiles and 20 attack drones.
The industrial hub, which had nearly one million inhabitants before the war, lies around 125 kilometres (78 miles) from the current front line.
The announcement of the attack on Dnipro came as Belgorod governor Vyacheslav Gladkov said at least five districts of his region in southern Russia had been repeatedly hit by Ukrainian forces over the last 24 hours.
The districts had been attacked by drones, mortars and artillery and the village of Kozinka was struck more than 130 times, he said.
In a rare attack on the southern Russian city of Krasnodar, two drones damaged buildings in the city centre, officials said, adding that there were no casualties.
The claims of fresh strikes in the Belgorod region came after an unprecedented two-day incursion from Ukraine claimed by two anti-Kremlin groups this week, with Russia using its air force and artillery to push back the fighters.
Russia's defence ministry has vowed an "extremely harsh" response to any further attacks on its soil.
The apparent exchange of artillery and missile fire reported on Friday came one day after Belarusian strongman Alexander Lukashenko said Russia had begun the transfer of nuclear weapons to his tightly controlled country.
The Kremlin, however, stopped short of confirming the start of the transfer, saying only Russia's ally was seeing "aggressive statements" from neighbouring countries.
"Belarus is in a very, very hostile environment," spokesman Dmitry Peskov told reporters.
In Washington, White House Press Secretary Karine Jean-Pierre described Russia's move as "yet another example of making irresponsible and provocative choices".
In Brazil, President Luiz Inacio Lula da Silva on Friday declined an invitation to travel to Saint Petersburg during a telephone call with Russian President Vladimir Putin.
"I thanked (Putin) for an invitation to go to the International Economic Forum in Saint Petersburg and replied that I cannot go to Russia at this time," wrote Lula on Twitter about the event scheduled for June 14-17.
China envoy in Moscow
Putin discussed Ukraine with the Brazilian president, telling him the Kremlin was "open" to dialogue and accusing Kyiv and the West of "blocking" talks, the Kremlin said.
Putin's top diplomat Lavrov hosted China's envoy Li, praising Beijing for its "balanced" position on Ukraine.
Li's visit to the Russian capital came after he met Zelensky in Kyiv earlier this month.
The foreign ministry in Moscow also made an official diplomatic protest aimed at the US embassy for what it said were recent US comments condoning alleged Ukrainian attacks on Russia and the annexed Crimean peninsula.
In Washington, the State Department said that US Secretary of State Antony Blinken will next week visit new NATO member Finland, where he will deliver a speech championing Ukraine's defence against Russia.
Earlier Friday, military officials in Kyiv said Russian forces launched aerial attacks on the capital overnight, adding that all the missiles were intercepted and destroyed.
"Another air attack on Kyiv, the 13th in a row since the beginning of May! And, as always, at night time," the city's military administration said on its Telegram account.