The US State Department dropped its diplomatic niceties and all but accused Russian President Vladimir Putin of lying about events in Ukraine, publishing a list of what it said were 10 of his "false claims".
A "fact sheet" released by the State Department's press office said Putin had ignored or distorted the facts in "justifying Russian aggression in the Ukraine".
The publication of the document, entitled President Putin's Fiction: 10 False Claims about Ukraine, is highly unusual for the State Department, which typically does not issue statements in public that a foreign leader is being untruthful.
Russia and the West face their most serious confrontation since the end of the Cold War over influence in Ukraine, a major commodities exporter and strategic link between East and West.
Ukraine pulled out of a trade deal with the European Union under Russian pressure last year, leading to months of street protests in Kiev and the February 22 ouster of President Viktor Yanukovych, a Russian ally.
Russia has since effectively occupied the Crimea region, where its Black Sea Fleet is based, further raising tensions in Ukraine, a former Soviet republic with a population of 45 million.
"As Russia spins a false narrative to justify its illegal actions in Ukraine, the world has not seen such startling Russian fiction since Dostoyevsky wrote, 'the formula "two plus two equals five" is not without its attractions," the State Department said in the document.
In the first of 10 bullet points, the State Department said: "Mr Putin says: Russian forces in Crimea are only acting to protect Russian military assets. It is 'citizens' defense groups,' not Russian forces, who have seized infrastructure and military facilities in Crimea.
"The Facts: Strong evidence suggests that members of Russian security services are at the heart of the highly organized anti-Ukraine forces in Crimea," the document continues.
"While these units wear uniforms without insignia, they drive vehicles with Russian military license plates and freely identify themselves as Russian security forces when asked by the international media and the Ukrainian military," it said, adding the forces carry weapons "not generally available to civilians."
The "fact sheet" posted on the State Department's website also takes issue with claims that there is a humanitarian crisis in Ukraine, that Russia's bases and ethnic Russians in the country are under threat, and that there have been mass attacks on churches and synagogues in southern and eastern Ukraine.
A US official speaking on condition of anonymity said the "fact sheet" would be translated into Russian.
Susan Rice, US President Barack Obama's national security adviser, also drew attention to it by sending a tweet that said: "Enough is enough with the Russian spin. Important we focus on the facts," and that linked to the document.
Spokesmen for the Russian embassy in Washington were not immediately available for comment.
CLINTON TAKES ANOTHER SWING
Putin is a tough but thin-skinned leader who is squandering his country's potential, former US Secretary of State Hillary Clinton said on Wednesday, a day after she likened his actions on the Crimean peninsula of Ukraine to those of Adolf Hitler in the 1930s.
Clinton, a potential 2016 presidential contender, warned during her latest speech at the University of California, Los Angeles that "all parties should avoid steps that could be misinterpreted or lead to miscalculation at this delicate time".
Putin has said he was protecting ethnic Russians by moving troops into Crimea.
However, Clinton said on Tuesday at a closed fundraising luncheon in Long Beach that Hitler had maintained that he was protecting Germans when he invaded places such as Czechoslovakia and Romania.
"Now if this sounds familiar, it's what Hitler did back in the '30s," Clinton said, the Press-Telegram of Long Beach reported. "Hitler kept saying, 'They're not being treated right. I must go and protect my people.' And that's what's gotten everybody so nervous."
Responding to a question submitted at the UCLA talk, Clinton said she was not making a comparison although Russia's actions were "reminiscent" of claims Germany made in the 1930s, when the Nazis said they needed to protect German minorities in Poland and elsewhere in Europe.
"I just want everybody to have a little historic perspective. I am not making a comparison, certainly. But I am recommending that we perhaps can learn from this tactic that has been used before," she said.
Clinton said Putin is trying to "re-Sovietise" the periphery of Russia but is actually squandering the potential of his nation and "threatening instability and even the peace of Europe."