Specialist mini jet engine makers across Europe are ramping up production and investment to head off a looming supply shortage that threatens to hold back Ukraine's rapid deep-strike drone program?at a critical stage of the war with Russia.

Mini turbojet drones are faster than propeller-driven models and far cheaper than cruise missiles, allowing Ukraine to strike deep inside Russian-held territory while competing with more advanced Russian systems such as the Geran-5.

But a shortage of the mini engines is raising concerns about a potential supply crunch for deep-strike drones, more than a dozen arms experts, companies and government officials said.