According to an international news portal the threat was discovered by the Washington Post newspaper, which obtained a copy of diplomatic correspondence sent by Moscow to the White House.

"We call on the United States and its allies to stop the irresponsible militarization of Ukraine, which entails unpredictable consequences for regional and international security," the note dated last Tuesday (12) reads.

According to the Journal, the diplomatic correspondence surfaced in the same week that Biden announced $800 million in extra military assistance to Ukraine.

Of note, the military aid package included artillery systems, armored vehicles and helicopters and brought the total American aid to Ukraine to over $2.4 billion.

"This new assistance package has highly effective systems that we have already provided and new capabilities. They are needed to contain the broader attack expected in eastern Ukraine," Biden said at the time in a statement.

Since the beginning of the war, tensions between the US and Russia have tended to escalate. Even the US president has accused Putin of being a war criminal.