NATO will start flying AWACS reconnaissance missions over Poland and Romania as part of the alliance's efforts to monitor events in Ukraine.
NATO ambassadors on March 10 endorsed the proposal from the alliance's top military commander, U.S. Air Force General Philip Breedlove.
A NATO official said the flights would "enhance the alliance's situational awareness."
The official made clear all the flights "will take place solely over alliance territory."
Ukraine's president fled last month after a deadly crackdown on antigovernment unrest, paving the way to a new government that Moscow has characterized as illegitimate.
Russian forces then occupied Ukraine's Crimean peninsula and the Crimean parliament voted to join Russia, creating a tense situation as pro-Moscow forces tighten their grip.
Based on reporting by Reuters and AFP