• US officials believe Ukraine is fostering a network of anti-Putin rebels in Russia, CNN reported. 
  • They also believe that such groups were behind the drone explosion over the Kremlin in May. 
  • Ukraine has not claimed any connection to such groups, but is reaping the military benefits.

Ukraine is believed to be behind a network of sabotage agents in Russia, smuggling drones into the country for a series of attacks, US officials told CNN. 

Several unnamed US officials believe the May 3 drone incident above the Kremlin was among several attacks carried out by such agents, the outlet reported. 

Russia has seen an increase in mysterious attacks and suspicious incidents on its soil ever since its invasion, many of which have taken place at strategic locations such as energy facilities within reach of Ukraine. 

Most recently, the border city of Belgorod came under a series of attacks that have been claimed by anti-Putin Russian dissident group the Liberty of Russia Legion, which opposes the invasion of Ukraine. 

Ukraine has not claimed any connection with these groups or any responsibility for similar attacks. 

Nonetheless, such actions are helpful for Kyiv, as the UK's Ministry of Defense assessed on Friday. "Russian commanders now face an acute dilemma of whether to strength defenses in Russia's border regions or reinforce their lines in occupied Ukraine," the MOD said, after the Belgorod attacks. 

Ukraine does have a pattern of making coy or celebratory comments about such events.

A Ukrainian security services spokesperson cited its head Vasyl Malyuk as saying: "We will comment on instances of 'cotton' only after our victory," according to CNN. "Cotton," in Ukrainian, is used as a slang term for explosion due to it sounding like "pop."

"Cotton" will continue, Malyuk added, per CNN.  

It is unclear exactly who in Ukraine is controlling these groups and whether the actions stem back to Zelenskyy, but US officials believe Ukraine's military intelligence is involved, CNN reported. 

There are multiple theories as to who was behind the incident at the Kremlin, where a drone appeared to cause an explosion over the building. 

Before many details of the incident had emerged, drone and strategy experts gave Insider various theories as to who could be behind it — including, potentially, Ukraine's conventional military; a Russian false flag; and Russian dissidents. 

Soon after, the US-based think tank the Institute for the Study of War assessed that it was "likely" a false flag attempt by Russia. 

Part of the reasoning was that Moscow had recently boosted its air defenses to such an extent that it would be very hard for a small drone to get through. 

But, CNN reported, some US officials believe that pro-Ukraine partisans could have launched the drone from within Russia, bypassing such defenses. 

This would have been possible due to smuggling networks that Ukraine has cultivated along its lengthy, difficult-to-police border with the country since as long ago as 2014, two unnamed sources told the outlet. 

Little damage was physically done to the Kremlin, but the target was highly symbolic and the explosion came a week before Russia's prized "Victory Day" annual military celebrations.

Kyrylo Budanov, Ukraine's military-intelligence chief, is said to appreciate symbolic gestures, officials told CNN.

However, some of his grander pronouncements — such as the claim in May 2022 that President Vladimir Putin is falling victim to a coup — have not been borne out in reality.