British military scientists sent hundreds of Indian soldiers into gas chambers to test mustard gas during more than a decade of experiments that began before World War II, a media report said.

British military did not check up on the Indian soldiers after the experiments to see if they developed any illnesses.

It is now recognised that mustard gas can cause cancer and other diseases, The Guardian reported on Saturday.

Many suffered severe burns on their skin, including their genitals, leaving them in pain for days and even weeks.

Some had to be treated in hospital.

The experiments began in the early 1930s and lasted more than 10 years at a military site in Rawalpindi, now in Pakistan, the paper reported, citing newly discovered National Archive documents.

The Indian troops were serving under the command of the British military at a time when undivided India was under colonial rule.

"Severely burned patients are often very miserable and depressed and in considerable discomfort, which must be experienced to be properly realised," it said.

The experiments in Rawalpindi were part of a much larger programme intended to test the effects of chemical weapons on humans, the paper reported.

The UK Ministry of Defence could not could not say whether the Indian soldiers were volunteers in the experiments.

It said: "The studies undertaken at the Chemical Defence Research Establishment in India included defensive research, weapons research and physiological research. These studies supported those conducted in simulated conditions in the UK in a different environment."