The Indian administration is expected to soon take up the proposal with Russian authorities.
Notably, Prime Minister Narendra Mod is scheduled to visit Russia in December, where he is expected to take up the matter with President Vladimir Putin. Also, Defence Minister Manohar Parrikar is expected to visit India's neighbour in the near future.
The S-400 is a new generation anti-aircraft system, which can be equipped with very long-range missiles (up to 400km), long-range (250km) and medium-range (120km).
The S-400 Triumf is capable of countering all air attack weapons, including tactical and strategic aircraft, ballistic missiles and hypersonic targets such as the US F-35 fighter jet.
India is likely to purchase 10-12 S-400s.
The S-400 can engage up to 36 targets simultaneously with as many as 72 missiles at altitudes of five meters to 30 km.