India has signed an over $5-billion deal to buy Russia’s S-400 aerial-defense system during Russian President Vladimir Putin’s visit to India. India earlier approved the deal to buy five units despite the US imposing sanctions against the country after Russia invaded Crimea in 2014. The US had warned India that buying Russian military equipment came under “focus area” for sanctions. India signed a $5.43 billion deal to purchase five advanced S-400 surface-to-air missile systems from Russia, defying threats of potential sanctions from Washington.The deal was finalized after Indian Prime Minister Narendra Modi concluded a summit with Russian President Vladimir Putin in New Delhi.The advanced air defense system can defend against different kinds of cruise and ballistic missiles. China was the first foreign nation to purchase S-400 systems.With its S-400 purchase, India now risks being sanctioned under Washington’s Countering America’s Adversaries Through Sanctions Act (CAATSA), which targets countries that purchase arms from Russia.During a joint media conference after their meeting, Putin said that Russia would work with India to boost bilateral cooperation in the United Nations, Shanghai Cooperation Organization (SCO) and G20.