He said this on the air of "Russia 1".
Gagin recalled that in order to seize the Crimea, it is first necessary to reach it, but it will be "very difficult" to do this because of the layered defense.
"I think a lot of people remember history: crossing the isthmus has always been such a bloody event for the stormer. I do not think that the Ukrainian army is ready for this, "RIA Novosti quoted the adviser to the head of the republic as saying.
In addition, the Ukrainian army is not ready for amphibious landings in the Crimea, because there is nothing to carry them out, Gagin claims.
"Therefore, you will have to go to the Crimea only on foot or by equipment, but the landscape itself will not allow this to be done with impunity and imperceptibly in any case," he concluded.
Deputy Chairman of the Russian Security Council Dmitry Medvedev said that the General Staff of the Russian Armed Forces is preparing its decisions in connection with the preparation of the Armed Forces of Ukraine for the offensive.
The Kremlin noted that crimea is an integral part of Russia and claims to Russian territory will receive a proper response.