NATO is strengthening its military footprint along its eastern border immediately in response to Russia’s aggression in Ukraine, the alliance’s chief said Wednesday.

Secretary General Anders Fogh Rasmussen said NATO’s air policing aircraft will fly more sorties over the Baltic region west of Ukraine, far from the tensions in the eastern part of the country. He said allied warships will also deploy to the Baltic Sea, the eastern Mediterranean and elsewhere if needed.

NATO’s supreme commander in Europe told reporters that ground forces could also be involved at some point, but gave no details.

NATO members Poland and the Baltic countries Lithuania, Estonia and Latvia have been wary following Russia’s annexation of the Ukrainian Crimean Peninsula, demanding a more robust military posture to counter neighboring Russia.

Rasmussen said the new NATO deployments are about “deterrence and de-escalation” in the face of Russia’s aggressive behavior in Ukraine, which is not a member of the 28-nation alliance.

The move was supported by the White House.

“We fully endorse the actions the alliance has taken to reassure NATO members and to bolster NATO’s presence in the Baltic nations,” White House spokesman Jay Carney said.

NATO estimates Russia has amassed some 40,000 troops on Ukraine’s eastern border and could invade if it wished. Fogh Rasmussen again urged Russia to pull those troops back.

The NATO chief did not mention naval deployments to the Black Sea — which Russia would likely see as a direct aggression even though NATO members Bulgaria, Romania and Turkey also border the sea.

But he insisted that “more will follow if needed.”

Air Force Gen. Philip Breedlove said multiple nations have approached him with offers of ground forces that will be included in a plan of operations he will give to NATO later Wednesday or Thursday.

Breedlove said the package of new military moves is designed to remain in place through Dec. 31.

“These measures are not a threat to Russia but they are designed to send a clear message that NATO will protect every ally and is ready to defend against any threat to our fundamental security,” Breedlove said.

He said he tried — but failed — to reach the Russian chief of general staff, Gen. Valery Gerasimov, to make that point.

NATO has already suspended most cooperation and talks with Russia.

(AP)