India's army made candidates at a recruitment day in Bihar take a written exam in their underwear to prevent them from cheating, reports said Tuesday, after a spate of exam scandals in the eastern state.

Images in the Indian Express showed dozens of men sitting cross-legged in a field clad only in underpants, with many resting their test papers on their thighs, while a uniformed supervisor stood guard.

The paper quoted an army source as saying they took the radical step to "save time on frisking so many people" after more than 1,000 candidates turned up.

"We had no option but to comply with the instructions even though it felt odd," one would-be recruit told the paper.

An army spokesman in New Delhi refused to comment on the report, which came a year after police in Bihar said they had arrested around 1,000 aspiring officers for paying people to sit their exams for them.

The High Court in the Bihar capital Patna on Tuesday asked the defence ministry for an explanation of the unusual move, after a lawyer filed a petition against the army.

Cheating -- using methods ranging from old-fashioned crib sheets to high-tech spy cameras -- is common in India, mostly to secure good school grades and highly-sought government jobs.

The impoverished state of Bihar, also one of the most populous, is especially notorious.

Last year a scandal in the state that saw relatives scale the walls of a school exam centre to pass notes to candidates went viral and made national headlines.

In the western state of Gujarat, authorities on Sunday blocked mobile phone Internet services in a string of cities and towns where entrance exams were taking place for public service jobs, to stamp out cheating.