At least six people were killed and more than 50 others were wounded in a barrage of Russian drones and missiles that struck several districts of Kyiv and brought down an apartment block, Ukrainian officials said.

One of the dead was a six-year-old boy, and Tymur Tkachenko, head of Kyiv's military administration, said the death toll could rise, with damage in more than two dozen locations.

The high-pitched hum of Russian drones could be heard for hours over the capital, interrupted by the occasional loud thunder clap of a missile strike.

Russian attacks have continued despite US President Donald Trump's threat to impose tougher sanctions on Moscow if Vladimir Putin does not agree to a ceasefire by 8 August.

Russia fired 309 drones and cruise missiles during the night, according to Ukraine's air force, and although air defences did manage to destroy some of the incoming fire, there were numerous hits.

A red-orange glow indicated destruction on the ground.

"One of the strikes hit a residential high-rise building, an entire entrance was destroyed. Rescuers are clearing the rubble," said Ukraine's interior minister Igor Klymenko.

Three of the fatalities were at the site of the apartment block.

"The world has yet again seen Russia's response to our, America's and Europe's desire for peace. More demonstrative murder," said President Volodymyr Zelensky. "This is why peace without strength is impossible."

Kyiv's Sviatoshynsky and Solomyansky districts were hit hardest in the attack, where one person was killed and 20 more were injured, according to Klymenko.

The windows of a hospital ward for children in Shevchenkivsky district were blown out by a shockwave, the mayor of Kyiv, Vitali Klitschko, said on Telegram.

One of Kyiv's higher education institutions, a school and a kindergarten were also damaged during the attack.

Foreign Minister Andrii Sybiha said it was a "horrible morning" in Kyiv, and that there are "still people under the rubble".

Sybiha added that Trump had been "very generous and patient" with Putin, but now it was time to put "maximum pressure on Moscow" through sanctions.

Earlier in July, Trump set a 50-day deadline for the Kremlin to reach a truce with Kyiv or risk economic penalties.

On Monday, during a visit to the UK, Trump cut that deadline to "ten or 12 days", expressing his disapproval at Putin's actions in Ukraine, more than three years since Moscow launched its full-scale invasion of the country.

Trump didn't say whether he felt the Russian president had been "lying" to him, but he said there was a discrepancy between Putin's rhetoric during their one-on-one conversations and the missiles "lobbed" on Ukrainian cities.

"We were going to have a ceasefire and maybe peace... and all of a sudden you have missiles flying into Kyiv and other places," Trump said.