• Ukraine said it stopped a Russian spy group gathering information on its F-16 fighter jets.
• The group wanted to find out details on the airfields F-16s may be using, it said.
• Ukraine said the group's leader was detained and other members indicted.

Ukraine said it disrupted a Russian spy ring that was collecting information on the F-16 fighter jets it was given by its Western allies.

The Security Service of Ukraine, or SBU, said on Tuesday that it had neutralized a network of Russian spies that was gathering information about military targets, including its F-16s.

According to the SBU, the group was tasked with trying to discover the locations of military airfields where F-16 fighter jets might be kept, as well as the locations of Ukraine's air-defense systems and companies that make electronic warfare systems to counter Russian drones.

It said the group was working across five regions in Ukraine and was deployed by Russia's Main Intelligence Directorate, or GRU.

It is not clear how much information, if any, the group was able to gather.

The SBU said its operation exposed 12 Russian agents and their informants.

Some of them were deserters who had left Ukraine's military and were recruited by Russia while hiding from punishment, it said, adding that they used their contacts, like Ukrainian soldiers in front-line areas, to try to gather intelligence.

Ukraine's Prosecutor's Office said one deceitfully recruited three soldiers he knew by pretending to work for Ukrainian intelligence, Pravda reported.

The SBU said agents who received the information would then go to the area of potential targets to gather extra intelligence.

According to Radio Free Europe, the group's organizer was detained and prominent members were indicted on charges related to state treason and the unauthorized disclosure of military information about the movement and location of Ukrainian forces.

Other members of the group could also face charges, the report said.

The SBU said suspects could face sentences ranging from eight years to life in prison, with their property confiscated.

The F-16s are the most powerful jets in Ukraine's arsenal, making them a major military and propaganda target for Russia.

Ukraine began receiving F-16s this summer, after repeated requests for the planes. Air warfare experts say the jets are a major boost to Ukraine's defenses, helping it protect cities and other targets from Russian drone and missile attacks.

Russia began targeting Ukrainian bases where F-16s could be kept before the first ones arrived, but there have been no reports of it successfully hitting bases when the jets have been present.

Despite their perceived importance, experts say Ukraine is not receiving enough F-16s to make a major difference, and it can't use them to launch raids or go on the attack unless it gets more.

The F-16s being given to Ukraine are also decades old — and are less powerful than Russia's best jets and the most advanced planes deployed by Ukraine's allies.