"Belarus is our strategic partner, we live in one Union State", Shugayev told reporters on the sidelines of the Eastern Economic Forum.
Since the S-400 was designed for export as well, "it would be logical to satisfy the needs of Belarus", the defence cooperation agency chief added.
Earlier in August, Belarusian President Alexander Lukashenko confirmed his country's interest in obtaining S-400s.
On 22 August, Russian Industry and Trade Minister Denis Manturov said that Moscow was ready to supply the missile systems to allied Belarus.
The S-400 is a road-mobile air-defence system capable of shooting down everything from planes, helicopters and drones to ballistic and cruise missiles at ranges up to 400 km.