Putin is on a two-day visit to India to attend the nineteenth Indo-Russia annual bilateral summit.
Besides the S-400 deal, India and Russian Federation are also expected to sign a number of crucial energy deals.
India's External Affairs Ministry says Putin and Indian Prime Minister Narendra Modi will hold talks on Friday and oversee the signing of a slew of agreements.
But Russia is still number one and is looking to remain so as India carries out a $100-billion upgrade of its military hardware to counter potential threats from China and Pakistan.
Alluding to the fact that CAATSA is only a way to grab larger part of the Indian defence pie, Ambassador Trigunayat said, "S-400 is essential for us".
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Jinnie Lee, a spokeswoman for the US Embassy in New Delhi, declined to comment on whether India would be granted a waiver, but said in a statement that the sanctions were "not meant to impose damage to the military capabilities of our allies or partners". Russian Federation accounted for 62% of India's arms imports during 2013-17. India had last month firmly told the United States at the "2+2" dialogue that it takes note of the historic nature of India-Russia defence relationship as also legacy issues and keep the missile deal out of the sanctions' regime.
Prime Minister Narendra Modi Friday invited Russian Federation to set up a dedicated defence industrial park in India as he looked to expand ties with New Delhi's traditional ally.
Putin said the two countries have agreed to step up cooperation in combating the menace of terrorism and drug trafficking.
Jinnie Lee, a US Embassy spokesperson, said that intent of US' implementation of Countering America's Adversaries Through Sanctions Act (CAATSA) is to impose costs on Russian Federation for its malign behaviour.
The threat of U.S. sanctions against buyers of Russian weapons - imposed most recently on China - is not expected to affect the Indian contract, which covers five regiments worth, Putin's foreign affairs aide Yuri Ushakov said. The deal demonstrates the highest level of trust and understanding between India and Russian Federation.
Last year India and China had a military standoff over a Himalayan plateau claimed by Beijing and Bhutan, a close ally of India.
Named after former Indian Prime Minister, Atal Bihari Vajpayee, the Atal Innovation Mission (AIM) is a flagship initiative school set up by India's policy think tank NITI Aayog to promote innovation and entrepreneurship among future generations.