The number of bodies found in mass graves has risen steadily in Mexico's escalating drug war [Reuters]

The Mexican Navy has said it has captured a suspected leader of the Zetas drug gang allegedly behind the mass killings of more than 100 people in northeastern Mexico.

Martin Omaar Estrada Luna, said to be the local leader of the gang, was captured on Saturday. He is accused of masterminding the murders of 145 people in Tamaulipas state near the US border.

Their remains were discovered in a mass grave earlier this month.

A navy statement said Estrada Luna, alias "El Kilo", is also the main suspect in the massacre of 72 central and south American migrants last August, also in the same township of San Fernando in Tamaulipas.

He was one of six people arrested in a navy operation on Saturday, the statement added.

A series of bus hijackings alerted authorities to the killings. Since April 1, officials have found about 20 mass graves in San Fernando alone.

The Zetas, a notorious gang formed in the 1990s by ex-military commandos, is now engaged in a fight to death with its former bosses.

Seven major drug gangs are operating in Mexico, and over 34,000 people have been killed since December 2006 in the raging wars for control over smuggling routes and government efforts to crack down on illegal activities.