Kyiv — Russia is running low on a key type of missile interceptor, sources tell CBS News, which could be helping Ukraine launch effective strikes deeper inside Russian territory as analysts note a possible changing of the tide in Kyiv's favor more than four and a half years into the war.

Moscow is experiencing a shortage of S-300 missile interceptors, three Ukrainian officials familiar with the country's intelligence estimates have told CBS News. The S-300, a surface-to-air missile system designed by the Soviet Union during the 1960s and 70s, has traditionally served as a vital component of Russia's air defenses against cruise and ballistic missiles. 

Throughout its war on Ukraine, Russia has turned to more advanced interceptors for that purpose, including the newer S-350, S-400 and Pantsir-S1 systems. But the S-300s have remained part of Moscow's defenses against Ukrainian missile and drone strikes. 

In 2025, estimates from Ukraine's intelligence services reported by The New Voice of Ukraine suggested Russia had more than 400 interceptors on hand for S-300PM and S-400 air defense systems.

The Ukrainian officials who spoke with CBS News this week did not specify how many interceptors Russia is still believed to have, but they noted a "reduction in Russia's stockpile of S-300 surface-to-air missiles," and suggested several possible explanations. 

While traditionally used exclusively for air defense, Russia's military has recently repurposed S-300s for offensive strikes on Ukraine, according to two officials. This has meant reconfiguring their trajectory so they work as surface-to-surface missiles, supplementing other Russian weapons systems such as the Iskander-M and Kinzhal ballistic missiles. 

Ukraine has also depleted Russia's stocks by forcing it to try and intercept regular volleys of newer, more capable drones, including some equipped with jet engines that are faster and fly further than older models. That has led Russia to expend interceptors it might otherwise have reserved to defend itself against Ukrainian missiles.

Ukraine has sought to exacerbate the shortages by directly targeting Russia's air defenses, analysts say. 

"In the last few months, Ukraine has destroyed or targeted a large number of air defense systems in the occupied areas — in Crimea, in Dniester, Luhansk, and elsewhere," said Rob Lee, a Russian military expert at the Foreign Policy Research Institute. "Many of Russia's air defense missiles are being used up very rapidly, at a kind of unsustainable rate, because Ukraine can produce more deep strike drones than Russia can, in some cases, produce air defense missiles."

Replenishing stocks may prove challenging for Russia. One Ukrainian official told CBS News that Moscow lacks key components to build interceptor missiles — including guidance seekers and control modules. The official said Russia, long under heavy sanctions, is encountering difficulties in obtaining such components from Western and Chinese manufacturers.

Ukrainian intelligence officials cautioned that Russia still has other capable, more modern air defense systems to defend against strikes. 

Moscow prioritizes "producing missiles for the more modern" air defense systems to counter Ukrainian drone attacks, Oleh Chornyi, the acting head of the Defense Intelligence of Ukraine (GUR), told CBS News.

And Ukraine has air defense problems of its own. Kyiv has sounded the alarm this year on its shortage of American PAC-3 interceptors, which are the most reliable defense against Russia's ballistic missiles. 

Fabian Hoffman at the Norwegian Institute for Defense Studies estimates that Russia may soon ramp up its production of ballistic missiles to 600 or even 800 per year. Lockheed Martin, which makes the PAC-3 interceptors used by Ukraine, only delivered 620 worldwide last year.

Still, the intelligence analysis suggesting Russian shortages comes amid wider assessments of a shift in favor of Kyiv on the battlefield.

As Ukrainian President Volodymyr Zelenskyy met G7 leaders in France this week, drones launched by his country struck an oil refinery deep inside Russia.

"This time, the Moscow region felt the reach of Ukraine's long-range capabilities," Zelenskyy said. "Russia must be forced to end its war against our people, and Ukraine's long-range weapons are one of the important components of such pressure."