Bilateral talks between Prime Minister Narendra Modi and Russian President Vladimir Putin have started in New Delhi. Both leaders are expected to announce the signing of key defence deals, including the purchase of S-400 Triumf missile system. The US has hinted at tough sanctions against any nation that buys advanced military hardware from Russia. India has indicated it would go ahead with the deal to acquire the S-400 long-range missile system, despite the US waning. Russia has been an important supplier of defence hardware to India for decades.