Analysts were agreed last night that the detonation of five nuclear bombs by Pakistan made the Indian sub-continent potentially highly unstable.
However, one analyst hoped that the new balance between the two countries might lead to dialogue.
Ms Rebecca Johnson, director of the Acronym Institute of London, said: "One potential way the situation could now move is that both countries, having proved they could set off a bomb, will start thinking about their national security and engage in regional confidence-building measures and bilateral talks to avoid military conflict that might escalate into nuclear war, and to avoid a nuclear arms race in the region. That is the one we hope happens.
"A second and very worrying possibility is that the war of the tests and the sizes of the tests escalates and causes a worsening of the conflict they already have in the Jammu Kashmir region.
"And if there is a nuclear arms race which develops from this in which both sides seek to develop missile-delivered nuclear weapons," she said.
The fact that both India and Pakistan had demonstrated their nuclear capability would also result in pressure for more effective nuclear disarmament across the board, she said. To avoid a nuclear arms race in South Asia, it would be necessary to delegitimise nuclear weapons everywhere.
In Washington, another analyst said he believed a chance still remained to move India and Pakistan from the nuclear brink - but that if either country moved to put warheads on missiles or aircraft, the arms race would escalate irreversibly.
"I see it as a real possibility that a future confrontation could involve nuclear weapons," said Mr Toby Dalton of the Carnegie Endowment for International Peace, citing the two countries' history of three wars in the past 50 years.
Once either country put a warhead on a missile or aircraft, escalation would become irreversible, he said.
"I think there is a chance - given enough strong international condemnation and intervention, and if the US rounds up China, Russia and its EU partners and helps India and Pakistan walk back from the brink - that we can stop it right here before it goes on any further," he said.
However, the international response to India's nuclear tests was tepid, and may have convinced Pakistan that it could weather economic sanctions, he said.