KYIV, June 27 (Reuters) - Russian missiles struck an apartment block and close to a kindergarten in the Ukrainian capital Kyiv on Sunday (Jun 26), in strikes US 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.