Moscow has deployed nearly 10,000 troops to the border with Ukraine, The Guardian reports on Friday, just days ahead of a planned Sunday referendum in Crimea and amid escalating tensions with the U.S. and the EU.

The Russian troop deployment comes as the U.S. beefs up its military role with Russia’s neighbors, including Poland and key Baltic states, in what some are calling a “containment strategy” reminiscent of the Cold War. NATO announced Monday it will begin flying reconnaissance aircraft over Poland and Romania to ‘monitor’ the situation in Ukraine.

The U.S. and EU have threatened Russia with new sanctions if the Crimea referendum moves forward.