A human rights group in Mexico says more than 600 soldiers have been detained at their barracks for the past 11 days and subjected to torture in an investigation into drug trafficking.

Soldiers from the 65th Infantry Battalion are being held in facilities in the city of Guamuchil in Sinaloa State, more than 1,000 kilometres (700 miles) from Mexico City, according to the non-governmental Mexican Front for Human Rights.

The soldiers "have been confined to the barracks, cut off from communication and subjected to torture and cruel and degrading treatment," said Benjamin Laureano Luna, the group's president.

Opium poppies are grown in Sinaloa State

He said he had been alerted to the alleged detention by wives of the soldiers, who had visited the barracks on Sunday.

Mexico's Defence Secretary General Gerardo Vega Garcia confirmed that some of the soldiers were under investigation for drug-related offences, but denied the other allegations.

"Nobody has been confined to base," he was quoted as saying.

Experts from Mexico's National Human Rights Commission have been dispatched to investigate the reports.

In the past, Mexican authorities have been seriously criticised for their use of torture as a key tool in investigations.

Combating drugs

General Garcia confirmed that about 48 soldiers were under investigation for drug trafficking.

He said the battalion was so corrupt it would probably have to be disbanded.

But despite what he called this week's "shameful event" and a series of other military drug scandals in recent years, General Garcia defended the army's role in anti-drug operations.

"Who could replace us, who else could do this work?" he said in a rare interview with local television network Televisa.

The 65th Infantry Battalion had been assigned to locate and destroy drug plots in the Sinaloa mountains.

Scores of drug distributors are said to operate in Sinaloa State, where marijuana and poppies - used in the production of heroin - are grown.