Kyiv, Ukraine - Donald Trump on Thursday called on Vladimir Putin to halt attacks on Ukraine, in a rare rebuke of the Russian leader after Moscow fired a barrage of missiles and drones at Kyiv, killing at least 12 in the deadliest attack on the capital in months.

The direct appeal to Putin came after Ukrainian President Volodymyr Zelensky urged his allies to put Russia under more pressure to halt its invasion.

The Ukrainian leader cut short a trip to South Africa to deal with the aftermath of the deadly strikes, the latest in a wave of large-scale Russian aerial attacks that have killed dozens of civilians.

"I am not happy with the Russian strikes on KYIV," Trump said on social media.

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"Not necessary, and very bad timing. Vladimir, STOP!" he said. "Lets get the Peace Deal DONE!"

Trump's envoy Steve Witkoff is due in Russia this week, where he is expected to hold talks with Putin on a possible deal, his fourth since Trump returned to the White House in January.

Ukraine has been battered with aerial attacks throughout Russia's three-year invasion, but deadly strikes on Kyiv, better protected by air defenses than other cities, are less common.

The attacks threw more doubt on already fraught US efforts to push Russia and Ukraine to agree to a ceasefire, with Trump having lashed out at Zelensky this week for not being willing to accept Russian occupation of Crimea, annexed by Moscow in 2014.

"We do everything that our partners have proposed, only what contradicts our legislation and the Constitution we cannot do," Zelensky told reporters in South Africa in response to a question about Crimea.

Zelensky also questioned whether Kyiv's allies were themselves doing enough to force Putin to agree to a full and unconditional ceasefire.

"I don't see any strong pressure on Russia or any new sanctions packages against Russia's aggression," Zelensky said, highlighting that Trump had previously warned of repercussions if Moscow did not agree to pause the fighting.

"The strikes must be stopped immediately and unconditionally," Zelensky said, calling Thursday morning's aerial assault "one of the most sophisticated, most brazen" of the entire war.