Following the "2+2" dialogue, which included Mattis" and Secretary of State Mike Pompeo's Indian counterparts, the two sides announced the signing of the COMCASA agreement, which Mattis said paved the way for sharing "sensitive technology' with India.
The pact enables high-transfer of power.
While finer details are still being worked out, some experts have cautioned that signing the deal might expose India's critical security communication to the United States.
"We see the Indo-Pacific as a free, open and inclusive concept, with ASEAN centrality at the core and defined by a common rules-based order that both our countries are pursuing", the minister said, adding India welcomed the US' interest in expanding its economic footprint in the region as they "complement our own efforts".
The agreement, which had been under discussion for more than a decade, will allow India to receive military-grade communications equipment from the United States and permit the exchange of real-time encrypted information on platforms used by the Indian and USA armed forces.
From left, Defense Secretary Jim Mattis, Secretary of State Mike Pompeo, Indian Foreign Minister Sushma Swaraj and Indian Defense Minister Nirmala Sitharaman deliver a joint statement after a meeting in New Delhi, Sept. 6, 2018.
In her opening remarks, Swaraj said she was confident the outcome of the talks will help unleash the untapped potential of the relationship between the two nations and further elevate the level of engagement.
But the two may contain China's influence by cooperating economically in a third country.
Russian military hardware accounted for 62 percent of India's total weapons imports during the past five years, the Stockholm Peace Research Institute said in a report this year. "And yet, they have managed to keep the differences on trade separate for the discussions, I presume", he said.
They come amid a series of divisive issues, including Washington's demands that India stop buying Iranian oil and Russian military supplies, and even news reports that President Donald Trump has mimicked the accent of Indian Prime Minister Narendra Modi. It provides for the lifting of sanctions imposed on Iran in connection with its nuclear program.
The government of Prime Minister Narendra Modi has notably chose to purchase Russian-made S-400 missile systems, despite US opposition, a move that US Defense Secretary James Mattis downplayed on his way to India this week. Other such deals can be expected during the dialogue, especially after the United States granted Strategic Trade Authorisation (STA-1) status to India.
The United States has emerged as India's second largest arms supplier, closing US$15 billion worth of deals in the past decade.
Some sanctions came in effect on August 6 and the rest, notably in the petroleum sector, on November 4.
MEA Spokesperson Kumar called the meeting between Swaraj and Pompeo a "productive" engagement.
A joint statement issued by the two sides mentioned the launch of a bilateral dialogue on the designation of terrorists in 2017, strengthening the action against terror groups, which reportedly includes "D-Company and their affiliates". The mechanism was agreed upon by US President Donald Trump and Indian Prime Minister Narendra Modi over the phone in August past year, but will only materialize after being cancelled twice for various reasons in April and July.