Ukraine's military is receiving counter-mortar radar systems from the United States as part of a $118 million equipment and training arrangement.

The Defense Department said the first three counter-mortar systems were delivered last week and that 17 more were on schedule for delivery over the next few weeks.

"The radar systems see incoming mortar fire and quickly calculate the point of origin of a mortar round fired by the enemy, and allows friendly forces to react appropriately," Pentagon spokesman Army Col. Steve Warren said.

The Ukrainian armed forces will determine how, where and when they will employ the systems, he said, and "it's also up to the Ukrainians if they attach these radar (systems) to a fire-direction system, which will allow for counter battery fires, or if they use them independently and react with ground forces."

Ukraine is battling Russia-backed secessionists in the eastern part of the country. Russia had earlier annexed Ukraine's Crimea region.

The Pentagon said U.S. personnel will soon begin training of Ukrainian soldiers on the systems.