Mexico City - Mexican investigators widened a probe into military corruption in the drug war, holding retired General Ricardo Escorcia and retired Lieutenant Colonel Silvio Hernandez in custody for alleged ties to a cartel.

The judge ordered them to a detention centre in Mexico City for 40 days while evidence is gathered, a spokesperson from the Federal Attorney General's Office said on Sunday.

A total of four high ranking military officers have been arrested and held this week in connection with the probe.

The arrests are the biggest scandal for the Mexican army since President Felipe Calderon took power in 2006 and launched a military crackdown on drug cartels.

According to media reports, the investigation centres on the Beltran Leyva cartel, which has smuggled tons of cocaine, marijuana, crystal meth and marijuana into the United States.

Among those detained in the probe is former deputy defence minister Tomas Angeles, who helped lead this offensive from 2006 until he retired in 2008.

A key strategy was to send soldiers onto the streets of troubled Mexican cities, such as Ciudad Juarez, across the border from El Paso. Soldiers have been accused of dozens of cases of torture and illegal killings during the offensive.

Since Calderon took power, around 55 000 people have been killed in drug related violence and more than 5 000 people have disappeared in Mexico. - Reuters