Santhanam, a former official with the Defence Research and Development Organisation, said that the thermonuclear or hydrogen bomb tests - the first and most powerful of the three tests conducted on May 11, 1998 - did not produce the desired yield.

R. Chidambaram, who was then the chief of the Department of Atomic Energy (DAE), is on record as saying that the bombs yield was 45 kilotons (45,000 tonnes of conventional explosive).

Santhanam's remarks are set to create a flutter in the non-proliferation establishment in the US and may raise fresh doubts about the future of the India-US nuclear deal which will unravel if New Delhi were to test again.

Santhanam's assessment is set to bolster India's opposition to signing the CTBT - an issue that may figure in the discussions when Prime Minister Manmohan Singh goes to the US in November. India has opposed CTBT on grounds that it is discriminatory and tends to divide the world into the nuclear haves and have-nots.