NEW DELHI: India will go ahead with the Rs 39,000 crore acquisition of five advanced S-400 Triumf air defence missile systems from Russia despite pressure from the US, asserted defence minister Nirmala Sitharaman here on Friday.India has now reached the "conclusive stage" in the procurement of the S-400 systems after negotiating the deal with Russia over the last few years, much before the recent US law called CAATSA (Countering America's Adversaries through Sanctions Act) came into force to deter countries from buying Russian weapon systems."I don't see it as choosing between the US and Russia…We have told the US Congressional delegation (that visited India recently) that we have had continuous relations with Russia, including defence procurements, which have endured for years," said Sitharaman, dismissing CAATSA as "a US law and not a UN law".TOI was the first to report in October 2015 that India had kicked off plans to acquire the S-400 missile systems, which can detect, track and destroy hostile strategic bombers, stealth fighters, spy planes, missiles and drones at a range of up to 400-km and altitude of 30-km.CAATSA will figure in the inaugural "two-plus-two" dialogue between Sitharaman and foreign minister Sushma Swaraj with their American counterparts, Jim Mattis and Mike Pompeo , which is now slated for early-September after its July 6 meeting was cancelled by the US due to scheduling problems.Both Mattis and Pompeo, incidentally, have argued for "national security waivers and relief" from CAATSA for countries like India, which has new military projects worth $12 billion with Russia hanging in the balance as well as the critical operational need to maintain the huge inventory of Russian-origin weapon systems in its armed forces.India and the US will also discuss bilateral military pacts like Communications, Compatibility and Security Arrangement (COMCASA) and the Basic Exchange and Cooperation Agreement for Geo-Spatial Cooperation (BECA), which are being pushed by the US for over 15 years now, in the two-plus-two dialogue.But Sitharaman said "final positions are yet to be arrived" in the discussions over COMCASA, which the US says will allow India more access to advanced military technologies and platforms with encrypted communications like Predator-B and MQ-9 Reaper drones."The two-plus-two meeting will be about developing and strengthening the strategic and defence cooperation between India and the US, how to go forward with LEMOA (the Logistics Exchange Memorandum of Agreement inked in 2016) and defence buys," said Sitharaman.