Washington "also wants to see a dialogue between India and Pakistan, dialogue that has expanded and has grown under the leadership of President Pervez Musharraf and others," State Department deputy spokesman Tom Casey said on Monday.

But "...this is not something that should be viewed as an action that we take with India that somehow requires a similar action in the case of Pakistan," he said in response to a question suggesting that Pakistan had test-fired another missile capable of carrying nuclear weapons to "challenge" the deal.

"And I think we've also been very clear that because of the issues with proliferation from Pakistan, that it's a very different situation between those two countries. And the fact that we have this agreement with India now is a clear recognition that there is a real difference," Casey added.

Repeating US Under Secretary of State Nick Burns' remarks on Friday on the formalisation of the 123 agreement, "the critical piece required under our law" to implement the nuclear deal, he said, "we believe that we have a relationship with India that's important and we have a relationship with Pakistan that's important."

"In the case of India, we've moved forward with this arrangement because, as the President said and as you heard from Nick on Friday, India has been a responsible actor. It's been outside the non-proliferation regimes, but it's actually behaved responsibly. It hasn't proliferated weapons technology. It hasn't done anything to undermine international assurances," Casey said.