Secretary of State Antony Blinken said the U.S. has made no concessions to the main Russian demands over Ukraine and NATO in a written response delivered Wednesday to Moscow.

Russia has demanded guarantees that NATO will never admit Ukraine and other ex-Soviet nations as members and that the alliance will roll back troop deployments in other former Soviet bloc nations. These are nonstarters for the U.S. and its allies.

Wednesday's answer to Russia makes very clear that the U.S. is standing by its principles, Blinken said. "There is no change, there will be no change.”

Russia has warned it would quickly take “retaliatory measures” if the U.S. and its allies reject its demands.

The Kremlin has repeatedly denied it has plans to attack Ukraine, but the U.S. and NATO are worried about Russia deploying an estimated 100,000 troops near Ukraine and launching a series of sweeping military maneuvers.

As part of the drills, motorized infantry and artillery units in southwestern Russia practiced firing live ammunition, warplanes in Kaliningrad on the Baltic Sea performed bombing runs, dozens of warships sailed for training exercises in the Black Sea and the Arctic, and Russian fighter jets and paratroopers arrived in Belarus for joint war games.

(The Associated Press contributed to this report.)