Russia has accused the US of direct involvement in the war in Ukraine for the first time.
A spokesperson for Moscow's defence ministry alleged the US was approving targets for American-made Himars artillery used by Kiev's forces.
Lt Gen Igor Konashenkov said intercepted calls between Ukrainian officials revealed the link.
There was no immediate comment on the allegation from US officials.
Russia previously accused Washington of fighting a "proxy war" in Ukraine.
"It is the Biden administration that is directly responsible for all rocket attacks approved by Kiev on residential areas and civilian infrastructure facilities in settlements of Donbass and other regions that caused mass deaths of civilians," Mr Konashenkov said.
Himars is a multiple rocket system which can launch precision-guided missiles at targets as far as 70km (45 miles) away - far further than the artillery that Ukraine previously had.
They are also believed to be more accurate than their Russian equivalents.
In April, Foreign Minister Sergei Lavrov said US President Joe Biden's decision to supply Ukraine with billions of dollars worth of arms meant "Nato, in essence, is engaged in a war with Russia through a proxy and is arming that proxy".
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