National security spokesperson John Kirby told reporters the United States will raise the development with the United Nations Security Council.

Kirby called North Korea's arms transfer to Russia a "significant and concerning escalation" and said the United States would impose additional sanctions against those facilitating these arms deals.

Kirby said Iran has not delivered close-range ballistic missiles to Russia but that Washington believes Russia intends to purchase missile systems from Iran.

Moscow has been heavily reliant on Iran for drones and other weaponry for use against Ukraine.

(Reporting by Jeff Mason, Steve Holland and Doina Chiacu; Editing by Chris Reese and Tomasz Janowski)