Russian missiles struck an apartment block and close to a kindergarten in the Ukrainian capital Kyiv on Sunday, in strikes U.S. President Joe Biden condemned as "barbarism" as world leaders gathered in Europe to discuss further sanctions against Moscow.

Up to four explosions shook central Kyiv in the early hours, in the first such attack on the city in weeks.

"The Russians hit Kyiv again. Missiles damaged an apartment building and a kindergarten," said Andriy Yermak, head of the president's administration.

A Reuters photographer saw a large blast crater near a playground in a kindergarten that had smashed windows.

Deputy Mayor Mykola Povoroznyk said one person was killed and six wounded. He said explosions heard later in other parts if Kyiv were air defences destroying further incoming missiles.

Russia has stepped up air strikes on Ukraine this weekend, which has also seen the fall of a strategic eastern city to pro-Russian forces.

"It's more of their barbarism," said Biden, referring to the missile strikes on Kyiv, as leaders from the Group of Seven (G7) rich democracies gathered for a summit in Germany.

Ukraine's Foreign Minister Dmytro Kuleba said G7 countries should respond to the latest missile strikes by imposing further sanctions on Russia and providing more heavy weapons to Ukraine.

As Europe's biggest land conflict since World War Two entered its fifth month, the Western alliance supporting Kyiv was starting to show signs of strain as leaders fret about the growing economic cost.

British Prime Minister Boris Johnson said the West needed to maintain a united front against Russian President Vladimir Putin.

"The price of backing down, the price of allowing Putin to succeed, to hack off huge parts of Ukraine, to continue with his programme of conquest, that price will be far, far higher," he told reporters.

At Sunday's G7 meeting, Britain, Canada, Japan and the United States proposed a ban on imports of gold from Russia.

MISSILES HIT CENTRAL CITY

Life had been returning to normal in Kyiv after fierce resistance held off Russian advances in the early phase of the war, although air raid sirens regularly sound across the city.

There had been no major strikes on Kyiv since early June.

In his nightly address, Ukraine President Volodymyr Zelenskiy said a wounded seven-year-old girl was pulled from the rubble of a nine-storey apartment block. The girl's father was killed in the strike, he said.

"She was not threatened by anything in our country. She was completely safe, until Russia itself decided that everything was equally hostile to them now - women, children, kindergartens, houses, hospitals, railways," Zelenskiy said.

A Ukrainian air force spokesperson said the strike was carried out with 4-6 long-range missiles fired from Russian bombers more than 1,000 kilometres away in the southern Russian region of Astrakhan.

Zelenskiy said on Sunday that Ukrainian defences had only managed to shoot down some of the 62 missiles that Russian had fired in the previous 24 hours and reiterated Kyiv's demand for partners to supply modern air defence systems.

Russian missiles also struck the central city of Cherkasy, which until now had been largely untouched by bombardment, according to regional authorities, who said one person had been killed and five others wounded.

Ukrainian presidential adviser Oleksiy Arestovych said the attack also hit a strategic bridge linking western Ukraine and the eastern battlefields. "They are trying to limit the transfer of our reserves and Western weapons to the east," he said in a message to Reuters.

Russia's defence ministry said it had used high-precision weapons to strike Ukrainian army training centres in the regions of Chernihiv, Zhytomyr and Lviv, an apparent reference to strikes reported by Ukraine on Saturday. There was no immediate comment about Sunday's strikes on Kyiv or Cherkasy.

Russia denies targeting civilians, but Ukraine and the West accuse Russian forces of war crimes in a conflict that has killed thousands, sent millions fleeing Ukraine and destroyed cities.

EASTERN BATTLEFIELD

The eastern battlefield city of Sievierodonetsk fell to pro-Russian forces on Saturday after Ukrainian troops retreated, saying there was no longer anything to defend in the ruined city after months of fierce fighting.

It was a major defeat for Kyiv as it seeks to keep control of two eastern provinces, Luhansk and Donetsk, that form the Donbas region, which Moscow demands Kyiv cede to separatists.

The military focus is now on Lysychansk, Sievierodonetsk's twin city, and the last major city held by Ukraine in Luhansk.

Tass news agency quoted a pro-Russian separatist official as saying Moscow's forces had entered Lysychansk from five different directions on Sunday and were pushing their way downtown, isolating the Ukrainian defenders.

Reuters could not confirm the report. Ukrainian officials said nothing about Lysychansk on Sunday.

The RIA agency quoted a pro-Russian separatist official as saying separatist forces had evacuated more than 250 people, including children, on Sunday from Sievierodonetsk's Azot chemical plant. The plant's surrounding industrial area was the last part of Sievierodonetsk held by Ukrainian forces.

Pavlo Kyrylenko, governor of the Donetsk region, said on the Telegram app that one civilian was killed and eight injured in Russian shelling on Sunday.

In the Ukrainian-held Donbas town of Pokrovsk, Elena, an elderly woman from Lysychansk in a wheelchair, was among dozens of evacuees who arrived by bus from frontline areas.

"Lysychansk, it was a horror, the last week. Yesterday we could not take it any more," she said. "I already told my husband if I die, please bury me behind the house."

GLOBAL FOOD SUPPLIES

Russia invaded Ukraine on Feb. 24 in what the Kremlin called a "special military operation" it said was needed to rid the country of dangerous nationalists and ensure Russian security. Kyiv and the West dismiss that as a baseless pretext for a land grab.

The war has had a huge impact on the global economy and European security, driving up gas, oil and food prices, pushing the European Union to reduce reliance on Russian energy and prompting Finland and Sweden to seek NATO membership.

Indonesian President Joko Widodo, who plans to visit Russia and Ukraine this week, said he would urge his counterparts to start a dialogue and would ask Putin to order a ceasefire.

"War has to be stopped and global food supply chains need to be reactivated," he said before leaving to attend the G7 summit.

The United Nations has warned that a protracted war in Ukraine, one of the world's major grain exporters, threatens to cause a global hunger crisis.

Reuters