American spy planes have reportedly been spotted by numerous aviation enthusiasts flying near Russian bases in Syria and Crimea on multiple occasions over the course of the last few years.

US P-8 Poseidon spy planes flying near Syria's territory have managed to intercept the operating frequencies used by Russian S-400 systems deployed at the Hmeymim air base in the Arab Republic, Russian Free News reported, citing Yuri Sytnik, a member of a Russian officers' NGO and experienced pilot. According to him, the American military still needs to decipher the data that they obtained before they can make use of it.

"Now they need to decrypt our S-400 systems' [codes], which operate [in Syria]. That's why we are driving [their planes] away. This is a common practice. They test our ability to drive them away. Reconnaissance in action", the pilot said.

Sytnik said that once the US cracks the code used by Russian S-400s, it will be able to mess with its operations, litter its radars with static, or even make it see planes that don't exist. It's also unclear whether all S-400s use the same frequencies.

The S-400s in Syria were deployed there in 2015 and have since guarded the Russian Hmeymim air base in the country from aerial threats, namely from drone swarms that terrorists have repeatedly used in their attacks.

At the same time, cutting edge Russian S-500 air defence systems use a different kind of radar compared to the S-400s, based on the use of X band frequencies and hence are likely to use frequencies different from those utilised by the earlier systems. The S-500s are expected to start being deployed with the Russian military in 2020.