India has paid US$800 million in one year after signing a US$5 billion agreement to buy these missile systems.
India has made an advanced payment of US$800 million for Russia's S-400 anti-aircraft missile systems, the Russian conglomerate Rostec said this week.
Sergey Chemezov, owner of the Russian company, told reporters Monday that negotiations were continuing at a good pace and that the contract with India will be concluded by 2025.
This development comes amid threats of U.S. sanctions, but New Delhi has pinned its hopes on an exemption from Washington.
India signed a US$5 billion agreement to purchase long-range surface-to-air missile systems in October 2018 during Russian President Vladimir Putin's visit to New Delhi.
At the BRICS summit in Brazil last Thursday, Putin reiterated that the S-400 deliveries to India were "on schedule.
In addition, Indian defense analyst, Ajai Shukla, told Al-Jazeera that "the United States has more or less indicated that it agrees with this project and is not likely to invoke sanctions against India as a result".
Moscow has long been India's largest supplier of military equipment, accounting for 62 percent of its total arms imports over the past five years, according to the Stockholm Peace Research Institute.
However, in recent years, New Delhi had moved closer to the U.S. and Israel in terms of new weapons.
The U.S. has issued threats to Turkey for the planned purchase of the same missile defense system.
Under a U.S. law, known as the Act to Counter U.S. Adversaries through Sanctions (CAATSA), the purchase of defense equipment from Russia may be subject to sanctions. However, the president may choose to issue an exemption.