(NewsNation) — Despite the U.S. sanctions against several Iranian entities for producing drones for Russia’s war in Ukraine, a retired Air Force lieutenant believes there is still cause for concern.

“Russia is now trying to get ready for a spring offensive but there’s a long war of attrition,” said retired Air Force Lt. Gen. Richard Newton. “The fact that Iran is now able to supply Russia with drones — and maybe surface-to-surface missiles later on — can enable Russia to stay in the fight much longer than perhaps we had anticipated.”

The sanctioned firms and other organizations were added to a U.S. export control list for those engaged in activities contrary to U.S. national security and foreign policy interests.

Watch the full interview with retired Lt. Gen. Richard Newton in the video above.

Reuters contributed to this story.