Russia has blamed the US and vowed "consequences" for a Ukrainian missile strike on Sevastopol in occupied Crimea on Sunday, which officials say killed four people - including two children.
Around 150 more were injured in the attack as missile debris fell on a beach nearby.
Russia's defence ministry said the missiles used by Ukraine were US-supplied ATACMS missiles, and claimed they were programmed by US specialists.
Kremlin spokesperson Dmitry Peskov called the strike "barbaric" and accused the US of "killing Russian children".
He pointed towards comments by President Vladimir Putin, who recently vowed to target countries supplying weapons to Ukraine.
Moscow said Sunday's deaths and injuries were caused by falling debris, after its air defences in Crimea intercepted five missiles loaded with cluster warheads launched by Ukrainian forces.
Footage carried on Russian state TV showed chaos on the beach in the Uchkuyevka area, as people ran from the falling debris and some injured people were carried away on sun loungers.
Russia's defence ministry claimed on Sunday that all ATACMS missiles are programmed by US specialists and guided by American satellites.
Foreign Minister Sergei Lavrov reiterated the claim during a meeting in Minsk on Monday, saying that the system "cannot be used without the direct participation of the American military, including satellite capabilities".
The US has been supplying ATACMS missiles to Ukraine for over a year. The system allows Ukrainian forces to strike targets up to 300km (186 miles) away, according to manufacturer Lockheed Martin.
Moscow illegally annexed Crimea in 2014 and just a handful of countries recognise the peninsula as Russian territory. It therefore does not fall under the US demands that Ukraine refrain from using Washington-supplied weapons to strike Russian territory.
A spokesperson for the White House National Security Council told the BBC: “Ukraine makes its own targeting decisions and conducts its own military operations.”
But Mr Peskov told reporters in Moscow on Monday that the "involvement of the United States, the direct involvement, as a result of which Russian civilians are killed, cannot be without consequences".
"Time will tell what these will be," he added.
The Russian foreign ministry summoned the US Ambassador Lynne Tracy on Monday, with Mr Lavrov claiming that US involvement in the attack was "not in doubt".
Moscow has repeatedly threatened to target countries supplying weapons to Ukraine, claiming that they are legitimate military targets.
Earlier this month, Mr Putin vowed to target countries arming Ukraine during a meeting with international news agencies.
"If someone thinks it is possible to supply such weapons to a war zone to attack our territory and create problems for us, why don't we have the right to supply weapons of the same class to regions of the world where there will be strikes on sensitive facilities of those (Western) countries?" he said.
"That is, the response can be asymmetric. We will think about it," he added.
Ukrainian officials have defended the strike in the wake of the attack, calling Crimea a legitimate target.
Mykhailo Podolyak - a top aide to President Volodymyr Zelensky - said the peninsula was in effect "a large military camp" which he said held "hundreds of direct military targets, which the Russians are cynically trying to hide and cover up with their own civilians".
The UN's human rights monitoring mission in Ukraine says at least 10,000 civilians have been killed since Russia invaded in February 2022. The real figure, officials say, is likely to be far higher.
BBC News
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