In addition to this denial, and the gloss of "self-determination" on the annexation of Crimea, Mr Putin's persistent disavowals of Russian military presence in eastern Ukraine have become staples of the Kremlin's script.
With these rhetorical acrobatics he and his senior officials have destroyed any diplomatic credibility they had, undermining the personal rapport among leaders needed for negotiations. Moreover, with basic facts disputed by their interlocutors, western officials find it almost impossible to engage in diplomacy about urgent geopolitical developments such as Moscow's military activities in Ukraine.
Yet Mr Putin's goal is not to deceive his counterparts. He knows western leaders have been briefed by their intelligence services, which have spy satellites and other capabilities that make it almost impossible to send tanks into Ukraine unnoticed. So why continue to lie?
The more compelling explanation is international. Russia is often denounced in the west as a revisionist power, determined to tear down the postwar international order. Given Moscow's flagrant violations of basic principles of international law, and its bilateral and multilateral commitments to Ukraine, these allegations have merit.
Yet if Russia were a truly revisionist power, its leaders would not be devising ever more creative ways to portray the country as a law-abiding actor. Instead of conducting a referendum in Crimea, no matter how preposterously biased, Mr Putin would simply have seized the peninsula without engaging in any procedure or any explanation. Rather than denying his invasion of Ukraine's east, this revisionist Putin would have been the first to announce his troops' progress across the frontier. And he would have had no hesitation in admitting that he would continue violating his neighbor's sovereignty as long as he deemed it in Russia's interests to do so.
None of this is to say that Russia's actions are anything but illegal and highly dangerous. But perhaps we in the west should not be so worked up about all the lying. It might be much worse for the international order if Mr Putin were to start telling the truth.