A day after President Barack Obama condemned the escalation of Russia's military intervention in Ukraine, President Vladimir Putin on Friday came out swinging with seven words: "It's best not to mess with us."
At a pro-Kremlin youth camp on the banks of a lake near Moscow, Putin struck a defiant pose: He touted Russia's nuclear arsenal, scoffed at criticisms of his March takeover of Crimea, and accused Ukrainian forces of behaving like Nazis in their five-month-old face-off with pro-Moscow separatists.
"I want to remind you that Russia is one of the leading nuclear powers," Putin said in remarks reported by Reuters.
The charged rhetoric comes amid a flurry of reports that Russia has invaded eastern Ukraine, which Putin has flatly denied.
Here's where things stand in the war of words between Putin and the West:
What is Putin up to in Ukraine?
NATO has said more than 1,000 Russian soldiers had joined the pro-Moscow separatists fighting the Ukrainian military. It also released satellite images showing Russian military equipment moving in Ukraine. The White House and Ukrainian leaders have accused the Kremlin of sending tanks, rocket launchers and armored vehicles to the rebel-held areas of Donetsk and Luhansk.
Putin refused Friday to answer those accusations. In a statement published on the Kremlin's official website, he instead hailed the pro-Moscow separatists, saying "the militia has achieved a major success in intercepting Kiev’s military operation."
He also called on the militia groups to "open a humanitarian corridor for Ukrainian service members who have been surrounded, so as to avoid any needless loss of life, giving them the opportunity to leave the combat area unimpeded and reunite with their families, to return them to their mothers, wives and children, and to quickly provide medical assistance to those who were injured in the course of the military operation."
Western analysts, however, are casting harsh scrutiny on Putin's recent actions.
"There's no question we're witnessing a significant escalation of the crisis," said Andrew Weiss, a Russia expert at the Carnegie Endowment for International Peace and an NBC News analyst.
Weiss said the pro-Moscow rebels, with Putin's backing, may be opening up a "third front" in the tumultuous conflict. He said it would appear the rebels are now pushing to the strategic port city of Mariupol.
By many accounts, the rebels have been steadily losing ground to Ukrainian military forces after they allegedly shot down Malaysia Airlines Flight MH17 over the Russia-Ukraine border July 17. The reported influx of Russian troops and tanks may be a way giving them a leg up, according to Yuri Shevchuk, an expert on Ukrainian language and culture at Columbia University.
What is the West's response?
A few American officials are bluntly pushing back against Putin's denials of a military incursion. Samantha Power, the Obama administration's ambassador to the United Nations, said Thursday the "mask is coming off" Russia.
“Russia has come before this Council to say everything except the truth,” Power said before the U.N. Security Council. “It has manipulated. It has obfuscated. It has outright lied. So we have learned to measure Russia by its actions and not by its words. In the last 48 hours, Russia’s actions have spoken volumes."
The U.S. ambassador to Ukraine, Geoffrey R. Pyatt, said in a string of tweets Thursday that Russian military aid to the pro-Moscow separatists had been insufficient, "so now an increasing number of Russian troops are intervening directly in fighting on Ukrainian territory."
At a news conference Thursday, President Obama said he expected to level more sanctions but stopped short of calling Putin's latest moves an all-out invasion. He said they were "not really a shift" but merely "a little more overt" forms of "what's been taking place for months now." He also said U.S. military intervention was not on the table.
“The separatists are backed, trained, armed, financed by Russia," Obama said. "Throughout this process, we’ve seen deep Russian involvement in everything that they’ve done.”
What is Putin's grand plan?
Putin rarely discusses his "end-game" in Ukraine, although he has said he wants to protect the country's Russian minority. In his remarks at the youth camp Friday, Putin compared Ukraine's military operations in the country's east to the Nazi siege of Leningrad during the Second World War.
"Small villages and large cities surrounded by the Ukrainian army which is directly hitting residential areas with the aim of destroying the infrastructure ... It sadly reminds me of the events of the Second World War, when German fascist ... occupiers surrounded our cities," Putin said.
But many Ukrainians and some Western analysts said Putin's real goal may be to build a so-called land bridge linking Russia and Crimea, the strategically valuable Ukrainian peninsula Putin annexed in March. That controversial move came after the Moscow-friendly government in Kiev was toppled in the wake of a rebellion over former President Viktor Yanukovich's rejection of a European Union trade deal.
A number of NATO officials have even suggested that Putin aims to essentially reconstitute the former Soviet Union. Shevchuk said it was no coincidence that Putin's remarks uploaded to the Kremlin website Friday were addressed to the "Novoroissya," or New Russia — a reference to Russia's historical claims to southern Ukraine.
"He is deploying the same kind of rhetoric that the Russian dynastic empires used," Shevchuk said. "It's deeply imperial. It's Putin's way of claiming that southern Ukraine has always been part of Russia."
Ukraine, meanwhile, appears to be trying to wrench itself from Putin's grip and move closer to Western security forces and European economic powers. The prime minister, Arseniy P. Yatsenyuk, on Friday announced that a bill had been introduced in Parliament to nix Ukraine's status as a nonaligned country and to “restore its aspirations to become a NATO member.”
“This law also reaffirms the main political goal of Ukraine — to become a member of the European Union,” Mr. Yatsenyuk said on his Facebook page.