By the BBC's Defence Correspondent
India's triple nuclear test raises the stakes in what has become a dangerous three-cornered regional arms race.
China, of course, is a declared nuclear power with a significant arsenal of weapons and various means to deliver them. Both India and Pakistan are thought to be capable of putting together nuclear weapons in a reasonably short space of time.
Neither country has actually claimed that it has deployed nuclear weapons. But these Indian tests underline the country's growing nuclear capability.
The nuclear arms race between India and Pakistan has spawned a parallel missile race as each country seeks to develop medium and long-range missiles that might carry a nuclear warhead.
Only a few weeks ago, Pakistan tested a new missile. And these Indian tests - threatened by the country's new government - may well in part be a response to this.
But China - and especially India's fear of China's arsenal - is the prime factor driving India's weapons programmes. The fact that Pakistan's own missile and nuclear programmes have had considerable Chinese assistance only adds to India's concerns.
The Indian tests represent a significant set-back for the Clinton administration's non-proliferation policy. Washington has spectacularly failed to restrain either India or Pakistan's nuclear ambitions.
And Washington is desperately seeking a lever that it can use to try to bring pressure to bear.
But Washington's own engagement with China adds another element of complication to this difficult problem.
Many Indian critics of the US position have insisted that if Washington really wants to stem the regional arms race, it should do more to encourage China to restrain the modernisation of its own