Joe Biden is sending more troops to eastern Europe amid growing fears Russia will invade Ukraine.
A US official has said the President is sending extra troops to Poland, Germany and Romania in response to the rising tensions between the two former Soviet nations.
It comes days after the White House approved additional military deployments.
Biden has directed more than 3,000 further U.S. troops to deploy to bolster European allies, according to reports.
About 2,000 American troops are said to be being deployed from the United States to Poland and Germany and about 1,000 will reposition from Germany to Romania.
The Pentagon has this week suggested that troop movements could come from within Europe.
Meanwhile, new satellite images suggest Russia has bolstered the overall readiness of its own military deployments in Belarus, Crimea and western Russia by bringing in more personnel and troops, a private U.S. satellite imagery company said on Wednesday.
The unverified images come from U.S.-based Maxar Technologies, which it said were taken from January 19 to February 1.
Moscow, which has massed more than 100,000 troops near Ukraine's borders, denies any plan to invade its neighbour but says it could take unspecified military measures if demands are not met, including a promise by NATO never to admit Kyiv.
In signs that, publicly at least, Russia is in no mood to signal compromise, the Kremlin mocked British Prime Minister Boris Johnson as "utterly confused" and ridiculed British politicians for their "stupidity and ignorance".
The Kremlin turned its rhetorical fire on Johnson, who cancelled a phone call with Putin on Monday to answer questions in parliament about boozy events in his Downing Street office during the Covid-19 lockdown.
Johnson visited Kyiv on Tuesday, where he accused Russia of holding a gun to Ukraine's head.
Kremlin spokesperson Dmitry Peskov said Russia had not announced any phone call with Johnson but added: "It makes sense to speak to anybody.
"Russia and President Putin are open to communicating with everyone.
"Even to someone who is utterly confused, he is prepared to provide exhaustive explanations."
Russia's foreign ministry went further, mocking Foreign Secretary Liz Truss for saying Britain was sending supplies to its "Baltic allies across the Black Sea" - two bodies of water that are on opposite sides of Europe.
"Mrs Truss, your knowledge of history is nothing compared to your knowledge of geography," Russian Foreign Ministry spokesperson Maria Zakharova wrote in a blog post.
"If anyone needs saving from anything, it's the world, from the stupidity and ignorance of British politicians."
It comes as RAF jets earlier today were scrambled to intercept unknown aircraft - thought to be Russian bombers - in a 'Quick Reaction Alert' mission.
Typhoon fighters from RAF Lossiemouth, supported by a Voyager Tanker from RAF Brize Norton, launched northwards against the "unidentified aircraft" approaching the "UK area of interest".
A Ministry of Defence spokesperson told the Mirror: "Quick Reaction Alert Typhoon fighters from RAF Lossiemouth, supported by a Voyager Tanker from RAF Brize Norton, have been launched against unidentified aircraft approaching the UK area of interest.
"We will not be offering any additional detail on this ongoing operation until complete."
