BRUSSELS >> NATO member countries today examined new ways to bolster the defenses of nations on the organization’s eastern flank as Russia’s military buildup around Ukraine fuels one of Europe’s biggest security crises in decades.

Over two days at NATO headquarters in Brussels, defense ministers were to discuss how and when to rapidly dispatch troops and equipment to countries closest to Russia and the Black Sea region should Moscow order an invasion of Ukraine.

U.S. Defense Secretary Lloyd Austin and his counterparts also plan to weigh the possibility of stationing troops longer-term in southeast Europe, possibly starting later this year. The troops would mirror the presence of some 5,000 servicemembers that have been stationed in allies Estonia, Latvia, Lithuania and Poland on a rotating basis in recent years.

The U.S. has started to deploy 5,000 troops to Poland and Romania. Britain is sending hundreds of soldiers to Poland and offering more warships and planes. Germany, the Netherlands and Norway are sending additional troops to Lithuania. Denmark and Spain are providing jets for air policing.

“The fact that we have deployed more NATO troops on the ground, more naval assets, more aircraft, all of that sends a very clear message,” NATO Secretary General Jens Stoltenberg said. “I think there is no room for any miscalculation in Moscow about our commitment to defending allies.”

The deployment has come in response to a formidable challenge.

Over the last four months, Russia is estimated to have amassed around 60% of its entire land forces and a significant portion of its air force to the north and east of Ukraine, as well as in neighboring Belarus. Moscow has appeared ready to repeat its 2014 invasion of Ukraine, but on a grander scale.

Russian President Vladimir Putin wants NATO, the world’s biggest security organization, to stop expanding. He demands that the U.S.-led alliance pull its troops and equipment out of countries that joined after 1997 — almost half of NATO’s 30-strong ranks.

NATO cannot accept his terms. It’s founding treaty commits to an “Open Door” policy for European countries that want to join, and a mutual defense clause guarantees that all members will come to the defense of an ally under threat.

Ukraine, though, is not a member and NATO, as an organization, is not willing to come to its defense.

“We have to understand that Ukraine is a partner. We support Ukraine. But for all NATO allies, we provide 100% security guarantees,” Stoltenberg told reporters ahead of today’s meeting.

That said, some member countries are helping Ukraine more directly, such as the U.S., Britain and Canada.

“We will be providing both lethal and non-lethal aid to Ukraine. This is a very significant issue for us all,” Canadian Defense Minister Anita Anand said.

But the “massive costs” promised to Putin should he order an invasion would be economic and political, mostly in the form of sanctions, which are not part of NATO’s remit. The alliance has offered Russia a series of security talks, including on arms control.

Over the last two days, Russia has said that it was returning some troops and weapons to bases, but Stoltenberg said the allies saw no concrete sign of a drawdown and concern that that Russia might invade Ukraine persists.

“They have always moved forces back and forth, so just that we see movement of forces, that doesn’t confirm a real withdrawal,” Stoltenberg said. “The trend of the last weeks and months has been a steady increase in the Russian capabilities close to Ukraine’s borders.”

He said the ministers agreed for military commanders to come up with new options for strengthening NATO’s defenses in southeast Europe near Romania.

“Moscow has made it clear that it is prepared to contest the fundamental principles that have underpinned our security for decades, and to do so by using force. I regret to say that this is the new normal in Europe,” Stoltenberg said.

France is set to lead one contingent in Romania, but the battlegroup is unlikely to be in place for several months, officials said.

Russia poses no direct security threat to any NATO country, but the alliance is concerned about the fallout from any conflict in Ukraine, like a surge of people fleeing fighting across European borders, or possible cyber and disinformation attacks.