It will cost India $5 billion (over Rs 40,000 crore), making it the country's largest defence deal.
The S-400 missile is world's one of the best air missile defence system that can destruct enemy missiles within the range of 400 KM.
Moreover, the Pentagon has warned India that the purchase would violate USA sanctions against Russia's military that went into effect this year.
United Kingdom authorities believe the Skripals door was targeted with the nerve agent Novichok. On Tuesday, Putin's top foreign policy aide Yury Ushakov had confirmed that the Russian President will oversee the signing of the S-400 air defence systems deal.
The US on Wednesday urged its allies not to enter into transactions with Russian Federation and warned that it would trigger American sanctions, a day after it was reported that India was planning to purchase multi-billion S-400 missile defence system from Moscow.
"We urge all of our allies and partners to forgo transactions with Russian Federation that would trigger sanctions under CAATSA", a State Department Spokesperson told PTI when asked about India's plan to purchase multi-billion S-400 missile defence system from Russian Federation.
"Two US Secretaries have written to the Congress strongly emphasising that countries not meant to be punished by the CAATSA (Countering America's Adversaries Through Sanctions Act) passed previous year by the US Congress should be granted the waiver", he said.
Turkey's Erdogan Says the USA has Taken the Wrong Path
He noted that Turkey lifted the state of emergency following the June 24 presidential and parliamentary elections in the country. But he expressed satisfaction that "both sides made a cautious attempt at rapprochement".
The US is in a hard position as it seeks to contain China through better ties with India, which like Washington has been unnerved by Beijing's growing assertiveness.
S-400 defence system is expected to boost India's defence along the country's borders with neighbours Pakistan and China.
Qatar, China and Saudi Arabia have already bought or are planning to purchase the anti-aircraft missile weapon from Russian Federation.
Besides, an inter-governmental agreement has been signed for Rosatom to construct another six reactors In India at a location yet to be finalised.
Russian state atomic energy corporation, Rosatom, is the consultant and equipment supplier for the Kudankulam Nuclear Power Project in Tamil Nadu, which envisages the construction of six 1,000 MW reactors.
Apart from S-400 missiles, Moscow is also likely to ink $2.5 billion deal for four more Krivak/Talwar class stealth frigates for the Indian Navy.
"It seems to me that our American partners make a colossal strategic mistake", he said, suggesting that the U.S. is undermining confidence and faith in the dollar as a universal tool.