New Delhi: U.S. sanctions on Russian military exports have put the brakes on a $6 billion deal with India and may derail the arms purchases of other U.S. allies around Asia, experts say.

Under a law that U.S. President Donald Trump signed in August, any country trading with Russia’s defence and intelligence sectors will face sanctions. The law is designed to punish Russian President Vladimir Putin for the 2014 annexation of Crimea from Ukraine, involvement in the Syrian civil war and meddling in the 2016 U.S. presidential election. But American allies who buy weapons and equipment from Russia, the world’s second-largest arms exporter, could suffer as well.

The highest-profile example is India, which wants to buy five S-400 long-range surface-to-air missile systems that the country’s military sees as a game changer. The systems are touted as being able to counter the ballistic missiles and stealth aircraft that China is developing while overwhelming the capabilities of Pakistan, India’s other main adversary.

The deal, which Putin and Indian Prime Minister Narendra Modi struck as part of an inter-government agreement in 2016, has run headlong into the U.S. sanctions law, two officials in Delhi said. A Russian source close to the Indian S-400 deal said “a lot will depend on the confidence and sanity of our Indian partners.”

Indian Foreign Secretary Vijay Gokhale and Defence Secretary Sanjay Mitra held discussions with U.S. officials in Washington last month to try to find a solution, a second Indian official said. The issue is crucial to the Indian military, because without Russian parts, supplies and maintenance help, “our ships won’t sail, our planes won’t fly,” the official said. “We can hardly be the regional security provider that America wants us to be at this rate.”

The United States has emerged as India’s No. 2 weapons supplier, closing $15 billion worth of deals over the last decade. Now Lockheed Martin and Boeing are leading the race to provide India with a fleet of new fighter-bombers, one of the world’s largest open tenders.