“We would like to see, obviously, in the regional sense in the relationship between India and Pakistan and others, a look at regional moratorium on fissile material production,” Rice told a congressional hearing on a landmark US-India civilian nuclear deal.

“We’ve made it very clear that we would encourage that; that we would encourage India and Pakistan to look at their nuclear relationship and the way that in some of the earlier days people were concerned about safety and security between the US and Soviet arsenals,” she said.

Fissile materials are plutonium or highly enriched uranium, which fuel nuclear explosions.

Rice was replying to Democratic Senator John Kerry on whether the United States could offer “real leadership” in trying to bring together the nuclear-armed neighbors, neither of which are signatories to the nuclear Non Proliferation Treaty (NPT).

Kerry, the failed Democratic candidate in the last presidential election, said that it was hard to understand why India and Pakistan would need to continue to build nuclear weapons at levels beyond an adequate deterrent between each other and China, an NPT signatory.

Kerry said he had raised this with Pakistani President Pervez Musharraf, and “there seemed to be a genuine spark of interest in the notion of trying to arrive at some agreement regionally on the numbers of nuclear weapons.”

Rice said the United States was unable to get a commitment on nuclear controls from the South Asian nations.

“Well, what we couldn’t achieve -- and I think it was unlikely -- was a constraint unilaterally by any one state,” she said.

“But the idea that has been pursued in some second-track arrangements, some second-track of discussions between the parties about not just absolute levels but also safety and security and confidence-building measures, I think is something we’re very interested in and we’d like to pursue,” she said.

US relations with India and Pakistan were improving rapidly ”that might make it worthwhile,” she added. “I can’t say that it’s going to have an immediate payoff. These things are hard.”

On the question of Washington seeking an arms control pact with India as part of the bilateral civilian nuclear deal, Rice said it was impossible to get such an understanding without including China and Pakistan.

“Therefore trying to use American leverage to get India to make this unilateral move is an idea that is certain to fail. It is a poison pill to kill any possibility for change,” she said.

Under the civilian nuclear deal, energy-starved India would gain access to long-denied civilian atomic technology in return for placing a majority of its nuclear reactors under international inspection.

India conducted nuclear weapons tests in May 1998 and Pakistan in a tit-for-tat response detonated its own devices a few days later.

The rivals have fought three wars, two of them over the Himalayan region of Kashmir.

After averting another war in 2002, they began talks to resolve their disputes, including Kashmir, in January 2004.

The two exchange lists of their nuclear facilities annually in line with a 1988 accord under which they agreed to refrain from attacking each other’s nuclear facilities in the event of a war.