Indo-US ties have deepened across 'a very broad spectrum' involving political, strategic and economic spheres and cooperation in counter-terrorism and defence sector, feels India's top diplomat here Meera Shankar at the end of her nearly two-and-a-half year tenure.

"Certainly the relationship has consolidated. And it is on a much better trajectory. But there is need for both countries to continue to engage in how we can build on the gains that we have made," Shankar told PTI.

The India-US relationship has deepened and expanded across a very broad spectrum -- political, strategic and economic, she said.

"Initially, the relationship began to grow in the economic field in the early 90s after the liberalisation in India because there were new economic opportunities which had not existed before. And then we saw that with the visit of (then) President (Bill) Clinton there was a greater political interest in India," she said.

This was taken further by former President George W Bush, particularly in his second term when the nuclear cooperation initiative was launched and that became "in a sense a vehicle for transforming the relationship," said Shankar, who will complete her tenure tomorrow and will be succeeded by Nirupama Rao.

Under the Obama administration, the two countries have completed various negotiations, including on reprocessing of spent fuel, she said when asked about the progress made on the landmark treaty between the two countries.

Shankar also noted that India's National Investigation Agency was given access to David Headley, who has confessed to his involvement in the Mumbai attacks, for questioning for almost a week, that revealed the full dimension of the conspiracy with regard to the 26/11 strikes.

"More recently we have seen the trial of Tahawwur Rana, where this information is part of the court record and in public domain as well. Overall, I will say that this will be a priority area of cooperation between the two countries," Shankar said.

In the field of defence cooperation, the two countries have a regular defence dialogue, training exercises, joint exercises and exchange of personnel.

The new dimension is the defence trade, because still about three-four years ago, India hardly had any defence trade relation with the US, Shankar said.

But as India has changed its own policies to look at making its procurements through international competitive bidding, "we have seen that American companies have also begun to take an interest and from the Indian side some of their equipment suitable to our needs," she said.

"So we have either bought or placed order for equipment worth USD 8 billion in the last three and half years. The most recent being C-17. And as I look ahead, I think, opportunities and partnerships (are) looking beyond defence trade to joint research and development to joint production to joint marketing."

"These are opportunities that lie ahead, and I am sure as we gain confidence in this relationship, we will be able to deepen the partnership to include areas like the ones that I have mentioned," Shankar said.

"A new area where we are looking to see where we can strengthen our trade cooperation is maritime security cooperation. That is one of the themes we discussed during the recent strategic dialogue that we had when Secretary Clinton visited India. Cyber security is the new area where we have launched dialogue," said the outgoing Indian Ambassador.