BRUSSELS — 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 and allied warships will 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’s members Lithuania, Estonia, Latvia and Poland have been wary following Russia’s annexation of Ukraine’s 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.

NATO Secretary General Anders Fogh Rasmussen addresses the media at NATO headquarters in Brussels, April 16, 2014. (photo credit: AP/Yves Logghe)

NATO Secretary General Anders Fogh Rasmussen addresses the media at NATO headquarters in Brussels, April 16, 2014. (photo credit: AP/Yves Logghe)

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.

He insisted, however, 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 present to NATO later Wednesday or Thursday.

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

He said he tried but failed to reach the Russian chief of general staff, Gen. Valery Gerasimov to say the measures are not a threat to Russia, but simply a message that NATO will protect its allies.

NATO has already suspended most cooperation and talks with Russia.

Copyright 2014 The Associated Press.