WATCH: Pentagon rejects ‘high-risk’ proposal for NATO nations to provide jets to Ukraine

WARSAW, Poland (AP) — The Pentagon on Wednesday slammed the door on any plans to provide MiG fighter jets to Ukraine, even through a second country, calling it a “high-risk” venture that would not significantly change the effectiveness of the Ukrainian Air Force.

Watch the briefing in the player above.

Pentagon press secretary John Kirby told reporters that Defense Secretary Lloyd Austin spoke with his Polish counterpart on Wednesday and told him the U.S. assessment. He said the U.S. is pursuing other options that would provide more critical military needs to Ukraine such as air defense and anti-armor weapons systems.

WATCH: White House press secretary Jen Psaki says U.S. won’t stop Poland from sending fighter jets to Ukraine

Poland had said it was prepared to hand over MiG-29 planes to NATO that could then be delivered to Ukraine, but Kirby said U.S. intelligence concluded that it could be considered escalatory and trigger a “significant” Russian reaction.

Kirby’s remarks went beyond his comments in a statement Tuesday, rejecting Poland’s offer to give fighter jets to the United States for transfer to Ukraine.

He said individual NATO nations can make up their own minds on what assistance to give Ukraine, but it’s questionable whether any would provide fighters without U.S. support.

Eric Tucker in Washington and Lorne Cook in Brussels contributed.