WASHINGTON (AP) -- The U.S. is planning to buy and send more medium- to long-range missile systems to Ukraine.

The hope is that the new systems will help Ukrainian forces hold onto the last remaining segments of land in the eastern Donbas that Russia has not yet been able to capture.

A senior defense official tells The Associated Press that Ukrainian forces are already effectively using advanced rocket systems, and more will go into Ukraine with trained troops soon.

An announcement is expected about the U.S. plan to buy and send a Norwegian-developed anti-aircraft system known as NASAMS.