A senior U.S. defense official said Friday that Ukrainian forces are using a U.S.-supplied rocket system to target Russian command posts.

In its fight for the eastern region of the country known as the Donbas, the Ukrainians have used the High Mobility Artillery Rocket Systems (HIMARS) advanced rocket system.

The official told reporters that theUkrainians are able to carefully select targets that will undermine the effort by Russia in a more systematic way.

Only a small number of Ukrainian troops can operate the systems after taking a brief training course, as the U.S. has already sent to the former Soviet country and four additional it promised late last month.

The Ukrainians have been able to hit distant targets with more accuracy with the help of the HIMARS.

They will be able to use this throughout the rest of the country.

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