Malaysia told India on Tuesday it will investigate accusations by Indian software professionals that police mistreated them during a raid to catch illegal workers earlier this week.

India called in Malaysia's envoy in New Delhi on Monday to demand an explanation for the police behaviour after some 270 people -- almost all Indian nationals barring a handful of Pakistanis -- were herded out of their apartment block in a dawn raid a day earlier.

Almost all of the Indians, who mainly worked in the information technology sector, were eventually released.

But many found their passports had been tampered with before being returned, with photographs scratched out and data on visa pages erased. A few also said they were physically abused.

Kuala Lumpur Police Chief Ahmad Bahrin Idris, according to state-run Bernama news agency, denied the Indians' allegations.

But Foreign Minister Syed Hamid Albar said Malaysia will investigate.

"We take such complaints very seriously and we will investigate and let the Indian government know the outcome of this investigation," Syed Hamid told reporters.

He said the police were still holding six Indians and three Pakistanis who have been unable to produce valid travel and work documents.

Aside from causing a wrinkle in relations with India, the incident has been a poor advertisement for Malaysia's efforts to establish a niche in the global knowledge economy.

The country suffers shortages of tech-savvy professionals, which India has in abundance.

Officials from the government-sponsored multi-media super corridor high tech zone joined in efforts with employers on Sunday to have the men released.

Malaysia depends heavily of foreign labour, but with a population of just 24 million people it fears being overrun with immigrants from poorer countries in the region.

Last year, hundreds of thousands of illegal workers from Indonesia and Philippines were deported. They mostly worked in construction, factories, agriculture and plantations, or as maids.

Crackdown meant for illegal aliens: Malaysia