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Putin says Ukraine attack is a ‘military action.’ Experts say it’s an invasion.

"He clearly wants to subjugate Ukraine," one expert said. "It’s deeply worrying and tragic.”

President Vladimir Putin has called Russia's attack on Ukraine a "military action" aimed at protecting Moscow supporters from a supposedly "genocidal" regime, but military and other experts say he's launched an invasion aimed at wiping an independent country off the map.

They say the evidence lies in the fact that Putin's forces are attacking Ukraine by air, land and sea, and targeting almost all of the major cities, not just the pro-Russian Donetsk and Luhansk enclaves in the eastern corners of the country.

"He wants to re-establish the Soviet Union," President Joe Biden said Thursday. "That's what this is about."

Russia is “making a move on Kyiv,” Ukraine's capital, a senior defense official told NBC News. Russia has “every intention of basically decapitating the government and installing their own method of governance.”

Putin's generals have used three main routes to invade their neighbor and capture key cities, the official said. In the south, they're moving from already Russian-occupied Crimea north to Kherson.

They have crossed the northeastern border of Ukraine and are heading south toward the city of Kharkiv, where some of the heaviest fighting has been reported, the official said.

And the Russian forces that had been deployed to neighboring Belarus are heading south to Kyiv, the official said.

The initial salvo of about 100 Russian missiles targeted military and air defenses, barracks, ammo depots and about 10 airfields.

"Putin is going to seize the entire country," retired U.S. Army Gen. Barry McCaffrey told NBC News. "This is an air, ground, sea military campaign" and the goal is seizing all of Ukraine "to the Polish border."

James Stavridis, a retired Navy admiral and former top NATO commander in Europe, and Michael McFaul, a former U.S. ambassador to Russia, said on NBC's “TODAY” show that the U.S. no longer has to guess about Putin’s “ultimate ambitions."

Russia’s actions are “the equivalent to Sept. 1, 1939, the beginning of World War II," McFaul said. "It doesn’t mean it’s going to blow up to be a world war, but this is the largest conventional war in Europe since 1939, and that has consequences not just for Europe, not just for Ukraine, but for the future of international stability writ large.”

"It certainly looks like Putin has broader ambitions than the two separatist entities, but the only person who actually knows is Putin himself," Paul Stronski, a senior fellow at the Carnegie Endowment for International Peace and an expert on Russia, said in an email, referring to the two breakaway regions in eastern Ukraine that Putin declared independent this week.

"He clearly wants to subjugate Ukraine, and appears to be targeting not just the cities/regions you’d expect, but Kyiv itself and ports in the south, and even out towards Western Ukraine," Stronski wrote. "It's deeply worrying and tragic."

Yohanan Petrovksy-Shtern, a Ukrainian native and professor of Jewish history at Northwestern University, agreed.

"Putin has been thinking about this for 20 years, talking about this for seven years, and is doing it now," said Petrovsky-Shtern, who also studied in Moscow. "Ukraine irritates Putin because it's a multiethnic democracy with its own culture and it is defying Russia. This is an invasion."

Petrovksy-Shtern added that he is from Kyiv and his mother is trapped there now.

The broad Russian offensive has plunged Europe into the gravest security crisis since World War II, and the Ukrainian government in Kyiv said it has heard reports that dozens of Ukrainian soldiers and civilians have already been killed.

Alexander Vindman, a retired Army lieutenant colonel and the former director for European Affairs for the National Security Council, said the Russians are also "prepared to take losses."

"Now they're moving into cities and they're going to sustain even heavier casualties," Vindman, who was born in Ukraine, told NBC News' Chris Jansing.

But Vindman, who became well-known after he testified against then-President Donald Trump at his first impeachment hearing, said he's already seeing "some early signs that this is a huge blunder for Vladimir Putin."

"I'm actually shocked how limited the strikes have been and how little effect they're having on (the) Ukrainian ability to resist," he said. "If this were the U.S. conducting these operations, we would eliminate all of the strategic nodes, we would degrade the ground forces before going in. The Russians clearly don't have that capability."

Retired U.S. Army Gen. George Casey said Putin "doesn't have the troops to occupy the country, especially if he wants to do it quickly."

"I think his objective is to carve out a land-bridge to Crimea through southeastern Ukraine by expanding the contested area in eastern Ukraine," Casey said in an email to NBC News. "I think the air and missile attacks on the larger cities in western Ukraine are diversionary."

Andrij Dobriansky, of the Ukrainian Congress Committee of America, which is based in New York City, said, "Putin wants his own version of Ukraine."

"He clearly wants to demonstrate some Russian shock and awe," said Dobriansky, referring to the military strategy that promotes the use of overwhelming speed and disinformation, among other things, to paralyze the opposition. "He wants to take all of Ukraine. Whether he can hold it all is a different story."

David Petraeus, a retired four-star Army general and former CIA chief, said that "we're still not sure sure how far President Putin wants this to go."

"He clearly wants to take control of Kyiv, to topple the current government of President (Volodymyr) Zelenskyy, to put a pro-Russian government in place," Petraeus said in a CNN interview.

Putin also appears to want to seize all of Ukraine east of the Dnieper River and "probably take control of the southern part of the country, the coastline, to take away Ukraine's access to the Black Sea."

Less certain, Petraeus said, is whether Putin will try to gobble up the western part of the country that borders Poland.

Poland, which has battled the Russians for centuries and was the first Soviet satellite nation to oust its Moscow-backed Communist government, belongs to NATO and has thousands of U.S. troops based there.