Seeking "expeditious action" on the civilian nuclear deal with India, the US has said that both sides should "now move forward" to complete the "important" agreement which is in their "best interests".

"I am very much involved in this agreement between India and the United States, and I've been in touch with the Indian government as recently as Thursday and Friday of last week," Under Secretary of State for Political Affairs Nicholas Burns said in London [Images], according to a transcript made available.

Burns was asked at the Foreign Press Association in London to comment on the status of the nuclear deal as also on a remark by the US Ambassador in New Delhi, David Mulford, that it is "now or never".

"It's an agreement that is entirely in the best interests of both countries. It's going to bring India out of its nuclear isolation dating back to the mid-1970s. It's going to allow civil nuclear trade of all countries with India: the provision of nuclear fuel, the construction of nuclear power reactors."

"It will allow India to go from 3 per cent reliance on nuclear energy, hopefully to say 20-25 per cent in a generation, with enormously positive benefits for global climate change and carbon  reductions in the process. So, there's a lot to like in this agreement," Burns said.

Now, the pact "has to be completed and I would say  that it's time to move this agreement forward. I do agree with Ambassador Mulford, our excellent American Ambassador in Delhi, we don't have all the time in the world. We are quite famously, in an election year in the United States. The Congressional calendar is crowded," Burns said.

"This agreement, after it's accomplished by the International Atomic Energy Agency and the nuclear suppliers group, needs to come back to the Congress of the US for one final vote," Burn said.

"We have broad bipartisan support, but it needs to get there, and so while I wouldn't want to say anything that would, in any way, intrude on domestic politics in India, from an international point of view, and given the fact that we're one of the negotiating partners, we do need to complete the agreement, and we're ready," the number three State Department official said.

Burns was pressed on whether it is "now or  never" for the nuclear deal as made out by Ambassador Mulford. He replied by saying, "I didn't say that".

When it was pointed out that the top American envoy in New Delhi had said that, Burns said  "I didn't say that. What I said was what I  said, that it's an important agreement and that we should now move forward to complete it.

"And that means that we would hope for expeditious action on this agreement by all concerned, including the Indian government," he said.