Top officials said Thursday that the US and Indian militaries will carry out large-scale joint exercises off India next year. The two countries' forces have not previously trained simultaneously in the air, on the land and at sea so, the drills would be a first of its kind. At the end of a summit, Defence Minister Nirmala Sitharaman made the announcement with US Defence Secretary Jim Mattis, Secretary of State Mike Pompeo and Indian Foreign Minister Sushma Swaraj. Ms Sitharaman said that they have decided to carry out a tri-services joint exercise with the United States off the eastern coast of India in 2019 for the first time. The two countries also signed a "Communications Compatibility and Security Agreement", known as COMCASA, that will enable them to exchange sensitive military information quickly and securely. Earlier on Friday , Mr Mattis and Ms Sitharaman signed the COMCASA agreement at a brief ceremony. The US only signs COMCASA agreements with trusted allies. Washington hopes to deepen its military ties with India. Washington however is concerned about an imminent deal India is making with Russia to buy the S-400 missile system. India and the US also took vows to enhance close cooperation in counter-terrorism operations.