The country said it would remain at the negotiations, but its opposition - as one of the three "nuclear threshold" states, with Pakistan and Israel - could delay adoption of the treaty for which negotiators have been striving for almost 40 years. India is one of eight countries - the five declared nuclear powers and three "threshold" powers - which the official nuclear powers want to ratify the treaty before it comes into force. India also refused to accept that provision yesterday.
The official nuclear powers believe that unless the treaty becomes law in the threshold states, which have nuclear weapons (Israel), or could build them easily (India and Pakistan), it will be meaningless.
India's Foreign Minister, IK Gujral, said: "The treaty as it has been drafted is a charade. If we want to rid the world of these weapons, then it is the five powers which have the weapons that have to do something." The stand means that the five nuclear-weapons states will have to make some concession to India, including a commitment not to build new nuclear weapons and a timetable for eventual nuclear disarmament. Either this or let the CTBT come into force without India.
The first discussion of an international nuclear test ban treaty began in 1958, and some arms control campaigners fear that if the 28 June deadline is not met, 40 years of work to reach a ban will have been in vain. But diplomatic sources last night said a further delay would not kill the treaty. India signed the Partial Test Ban Treaty (PTBT) in 1963, which prohibited tests in the atmosphere. In 1974, it conducted a so-called "peaceful nuclear explosion" under the Rajasthan desert,but since then has not exploded a nuclear device. The US State Department, however, warned that India could have been preparing to conduct a test there earlier this year.
Assembing a workable nuclear device quickly shouldpose no difficulty to India. Pakistan, with which India has fought three wars since 1947, has a proven missile-warhead design and could also assemble weapons quickly. India envisages keeping separated components of nuclear weapons that can be assembled for a "second strike" in response to attack by Pakistan or China.
When the CTBT was first proposed, a ban on testing would have acted as an effective constraint on the development of new weapons by the established nuclear powers and on nuclear proliferation. To ensure new nuclear weapons worked it was necessary to test them, and the nuclear stockpiles, too, to check they still worked. However, modern computer simulation techniques have made tests unnecessary. France's nuclear tests in the Pacific last year were the last, and Monday's agreement between France and the US to share nuclear data has further obviated the need for tests.
Some experts also question whether India would need to test nuclear weapons. Pravin Sawhney, a former Indian Army officer and a research fellow at the Royal United Services Institute in London, said India could, without tests, build "boosted- fission" devices - nuclear fission bombs with a fusion component similar to the first British "H-bombs", and with a yield of up to 500 kilotons.
"The Indian government has invested heavily in super-computing and related software," Mr Sawhney wrote in the Institute's journal.