Ukrainian intelligence said Cuban fighters are paid an average monthly wage of $2,000, but that foreign mercenaries typically die within five months.

Ukraine is making progress in intensive talks to formalise legally binding security guarantees with the United States and European allies, a key part of its bid to end the war with Russia, First Deputy Foreign Minister Serhii Kyslytsia said.

Drones used for defense and attack have taken a central battlefield role in the more than three years since Russia invaded Ukraine.

Ukraine's defense industry is setting up shop in Denmark, offering Kyiv's arms makers protection from Russian missiles and bringing their battlefield know-how to Europe.

Russia Gaining In Drone War, Forcing Ukraine To Adapt is published in Aerospace Daily & Defense Report, an Aviation Week Intelligence Network (AWIN) Market Briefing and is included with your AWIN membership. Already a member of AWIN or subscribe to Aerospace Daily & Defense Report through your company? Login with your existing email and password.

"If any troops appear there, especially now while fighting is ongoing, we assume that they will be legitimate targets," Putin says as the U.S. and Europe plan for a post-war Ukraine.

Ukraine has ramped up strikes on energy sites to increase pressure on Russia, which relies on revenue from oil and gas exports.

"If it had all happened at once, maybe you could call it an accident. But six hours of drones? That’s a test – a way to see what the West would do. And we have to respond like it’s a test," Kellogg said.