The AWACS (Airborne Warning and Control System) flights will take place solely over NATO territory, the alliance said on Monday.
Ukraine is not a NATO member but Russia's intervention in Crimea has alarmed neighboring countries, including alliance members that used to be dominated by the Soviet Union.
The announcement comes as the United States is sending a dozen F-16 fighter jets and 300 service personnel to Poland as part of a training exercise.
The US and Russia are bitterly divided over how to ease the crisis, with each challenging the other to show they are really interested in a peaceful outcome.
Russia denounced alleged lawlessness by far-right activists in eastern Ukraine on Monday, in a statement likely to trigger fear in Ukraine over possible Russian intervention.
The Russian Foreign Ministry said it was outraged by lawlessness in the country’s east, blaming the group Right Sector for "conniving" with the new government in Kiev.
Right Sector is a grouping of several far-right and nationalist factions who were actively involved in the uprising against Moscow-backed President Viktor Yanukovich.
BA/BA