Hagel told the Senate Armed Services Committee that a U.S. aviation detachment posted in Poland would increase its joint training and that the U.S. would augment NATO’s air policing mission over the Baltic peninsula.

The Air Force is planning to send six more F-15 Eagle fighters and one KC-135 refueling tanker to Lithuania this week “at the request of our Baltic allies,” a defense official said. Those aircraft will join four F-15s that already were taking part in the air policing mission.

( PHOTOS: Ukraine turmoil)

The Pentagon has previously announced it has canceled its military-to-military plans with Russia, including two previously scheduled exercises that would have involved Canada and Norway.

But Hagel repeated to senators President Barack Obama’s message that the best response to Russia’s incursion into Ukraine was not with a military option.

“This is a time for wise and steady and firm leadership, and it’s a time for all of us to stand with the Ukrainian people in support of their territorial integrity and their sovereignty and we are doing that,” he said. “That, in particular, is what President Obama continues to do as we pursue diplomatic and economic options.”

The next major milepost in the storyline was the meeting Wednesday in Paris between Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov. Hagel, who has already spoken to his Russian counterpart, said he expected there would be more discussions of the United Nations Security Council, NATO members and other international bodies worried over the Ukraine crisis.

( WATCH: Driving the Day: Hill, business brace for Ukraine aid)

Later, NATO announced it too was suspending its dealings with Russia and that the alliance’s entire relationship was “under review.”

Joint Chiefs Chairman Gen. Martin Dempsey, who appeared with Hagel on Capitol Hill, told senators he’d spoken to his counterpart in Moscow earlier on Wednesday.

“I conveyed to him the extent to which Russian territorial aggression has been reputed globally and urged restraint,” Dempsey said.

Hagel said a proposed international package of aid and loan guarantees for Ukraine “is a particularly important part of this.” A short-term cash infusion for Kiev, supporters say, is a shot in the arm it needs to get out from under immediate Russian economic pressure and to stabilize the interim government there.

The wild card in the Ukraine crisis remains Russian President Vladimir Putin, whose goals and motives in sending troops into the Crimean peninsula remain known only to him. Putin claimed this week that Russia was acting in defense of Russian-speaking or Russian-aligned peoples inside eastern Ukraine, to which American leaders have responded incredulously.

Obama responded to Putin’s claim that he was within his rights by reaffirming Washington’s belief that Russia had violated international law.

“I know President Putin seems to have a different set of lawyers making a different set of interpretations, but I don’t think that’s fooling anybody,” Obama said on Tuesday.

Sen. Roger Wicker (R-Miss.) asked Hagel and Dempsey whether they had talked about Putin’s claims with their Russian counterparts — specifically the Russian claim that it had no troops at all in the Crimea. And Dempsey said he had.

“The answer was they were not regular forces, they were well-trained militia forces responding to ethic threats in the Crimea,” Dempsey said dryly. “I did suggest that a soldier looks like a soldier looks like a soldier and that distinction had been lost on the international community.”

Dempsey told the committee he believed the approximately 16,000 troops occupying the Crimea were regular Russian soldiers who had been “taken out of their traditional uniforms” and were, in effect, pretending to be the local militia that Moscow claims is responsible for the presence of armed men there.

Wicker also asked whether Washington might be willing to go along with Russian control of the Crimea, or even the prospect of additional incursions by Russia into the eastern portions of the country. No, Dempsey said, citing the 1994 Budapest agreement under which Ukraine surrendered its Soviet-era nuclear weapons to Moscow in exchange for a guarantee of its sovereignty and territorial integrity.

“I don’t find any ambiguity about that,” Dempsey said.

Even though the Obama administration says the best response remains diplomatic, Dempsey told senators the Ukraine crisis showed the value of keeping the military ready for any eventuality.

“Russia’s actions remind us that the world today remains unpredictable, complex and quite dangerous,” Dempsey said. “We cannot think too narrowly about future security challenges, nor can we be too certain that we have it right. The world will continue to surprise us, often in unpleasant ways.”

The Armed Services Committee’s top Republican, Sen. Jim Inhofe of Oklahoma, put a finer point on it. Reducing defense spending, he argued, only increases the risk of instability around the world as unstable actors feel safer to step out of line.

“I think that means we’ll have more events like Ukraine,” he said.