The alleged incident has again shaken faith in a controversial national service programme, launched in 2004, to foster national unity by recruiting all Malaysians, including those from ethnic minorities.

Basant Singh, 17, said his hair, which had reached below his waist, was cut as he slept at a training camp in northern Penang state.

"I was fast asleep on Sunday night. When I woke up the next day, I realised that my hair had been cut off as I was about to tie it," Singh was quoted as telling The Star newspaper.

The incident has caused deep concern among Malaysia's 150,000-strong Sikh community -- a minority in the Muslim-majority country -- for whom cutting hair is forbidden.

In a sign of the sensitivities in a country where minorities say their rights are being eroded by rising "Islamisation", authorities immediately launched a two-week probe into the case.

"We will investigate. We will do a thorough probe. I don't want to speculate (as to what happened)," Abdul Hadi Awang Kechil, director-general of the national service training department, told AFP Wednesday.

Basant's father, 46-year-old Sikh religious leader Surinderpal Singh, said his son had become withdrawn since the incident, in which his hair was cut by 50cm (20 inches).

"He is quite traumatised as I have taught him never to cut his hair," he told AFP, adding that he would not allow his son to continue in the national service programme as he feared for his safety.

"My friends are deeply hurt. It is a tragedy that has happened not just to an individual, but to our Sikh community," he said.

Harcaran Singh, president of the Malaysian Gurdwaras Council, a Sikh representative body, said the probe must seek to determine who was involved in the hair-cutting and what their motives were.

"It is not a trivial issue. It must be nipped in the bud. This kind of incident will erode confidence in the national service programme," he said.

The military-style national service programme for 18-year-olds, compulsory for three months for those selected by lottery, was launched in 2004 to boost patriotism and racial integration.

However, the scheme has been beset by problems including unsafe campsites and the death of 16 trainees, triggering calls for its closure.