Fox News military analyst Gen. Jack Keane (Ret.) weighed in this morning after U.S. paratroopers began arriving in Poland in a show of U.S. support for NATO allies in eastern Europe.

Here's more on the move from

Pentagon press secretary Rear Adm. John Kirby said an initial contingent of about 600 troops will head to four countries across Eastern Europe for military exercises over the next month. 

First, about 150 soldiers from the 173rd Airborne Brigade Combat Team based in Vicenza, Italy, are arriving in Poland. 

Additional Army companies will head to Estonia, Latvia and Lithuania and are expected to arrive by Monday for similar land-based exercises in those countries. 

The show of strength comes as the United States, European allies and Ukraine try to ease tensions with Russia and pro-Russian separatists in eastern Ukraine. All sides struck a diplomatic agreement last week, but it remains unclear whether pro-Russian demonstrators, who took over a series of government buildings in the wake of Russia's annexation of Crimea, will back down. 

Under the current plan, U.S. troops would rotate in and out of the four Eastern European countries for additional exercises on a recurring basis. 

"We're looking at trying to keep this rotational presence persistent throughout the rest of this year," Kirby told reporters, adding that over time the exercises could expand to other countries. 

Meantime, pro-Russian forces are continuing to move throughout eastern Ukraine as the Pentagon says it sees nothing to indicate Russian President Vladimir Putin has any intention of deescalating the tension.

Keane said he welcomes the U.S. troop exercises, calling it "an important step in the right direction."

"The symbology of it is absolutely clear. Not only reassuring our allies, but sending a message loud and clear to Putin and his folks that if you cross that border into one of these countries, you're at war with NATO and specifically the United States," said Keane.

He continued that what will happen next is up to Putin, but he's not going to back away in Ukraine unless the sanctions get "a lot tougher." Keane said the current policy is all about deescalating the situation, but it should be more focused on confronting and isolating Putin.

"We have to accept some of the risk of those consequences," said Keane.

He called for tougher sanctions on the Russian banking system and energy companies, along with hundreds more of Putin's cronies.

Watch the full analysis above.