Washington: The United States has said the landmark Indo-US nuclear deal signifies a 'qualitative' change in bilateral relations between New Delhi and Washington and one that cannot be compared with any ongoing nuclear programme elsewhere.

".It opens up quite obvious possibilities in the nuclear energy sector. But it is also certainly symbolic of a new chapter in US-Indian relations," State Department Spokesman Sean McCormack told reporters here.

"I think it certainly signifies a qualitative change in our relationship that has been building for quite some time, but there were certain obstacles for it to actually proceed to the next stage. And one of these was this issue of India's nuclear program and how it related to the rest of the world on that ith regard to that issue, and then other issues," he said.

"We think that it is quite important. It was a quite important moment," the official said.

Noting there are areas in the Indo-US relations that have to be broadened, he said, "I think you'll probably see more activity in that regard from the Secretary as well as others in the Administration in the months ahead".

"There's still work to do, mind you, in terms of negotiating some of the agreements, 123 agreement, and then India also has to negotiate a separate agreement with the IAEA, and then the Nuclear Suppliers Group has to act," he said.