Mexican troops arrested a leading member of one of the country's two main drug gangs and seized nearly a million dollars, a victory in President Felipe Calderon's fight against traffickers.

Soldiers detained Alfredo Beltran Leyva on Sunday in a plush area of the northwestern city of Culiacan, a spokeswoman for the attorney general's office said.

Beltran Leyva and three other people arrested with him were carrying about $900,000 in cash in two suitcases. "Among his key functions was transporting drugs, money laundering and bribing officials," the spokeswoman said on Monday.

Prosecutors say Beltran Leyva is a lieutenant of Joaquin "Shorty" Guzman, Mexico's most wanted man and the head of an alliance of smugglers based in Sinaloa state.

The United States, whose Congress is debating sending surveillance and detection equipment to help Mexico's year-old drug crackdown, praised the arrest, with Ambassador Tony Garza calling it a "significant victory."

The Sinaloa gang is in a bitter fight with the rival Gulf Cartel, based south of Texas, for control of smuggling routes.

More than 2,500 people died in gangland-style killings last year as Calderon launched an army crackdown on drug cartels. Many of the killings were gruesome, with victims often tortured or beheaded and their bodies left in the street.

Beltran Leyva, who has four brothers also accused of being powerful traffickers, was the head of two teams of hitmen known as "The Baldies" and "The Blondies" in two western states.

The Baldies have battled the Gulf Cartel in shootouts in the beach resort of Acapulco that have horrified residents and tourists in recent years.

VIOLENCE UNABATED

Calderon has deployed 25,000 troops and federal police to crush drug cartels in a year-old crackdown that has had mixed results. Scores of traffickers have been arrested, and some extradited to the United States, but violence has not abated, with police, soldiers and public officials often targeted.

On Monday, gunmen in the northern city of Monterrey killed a local judge who had sent at least one high-profile drug gang member to jail. The hitmen fired at the judge as he drove down a busy street in the north of the city, Mexican media said.

Drug hitmen last week broke traditional codes of honour against killing children when they murdered a 3-year-old boy and a girl aged nine in the tough border city of Tijuana.

The killings were despite the government sending hundreds of police and army reinforcements to Tijuana in January to stamp out a surge in drug violence there.

U.S. Attorney General Michael Mukasey said on a visit to Mexico last week that the spurt in killings emphasized the need to keep up pressure on "drug terrorists" and pledged tighter controls on U.S. guns flowing across the border illegally.

Calderon extradited the head of the Gulf Cartel, Osiel Cardenas, to Texas a year ago and police seized $206 million from the house of a drug suspect in Mexico City in what they said was the world's biggest drug cash haul.

But No. 1 suspect Guzman, who escaped from a high-security jail in 2001, still evades police, as does ally Ismael "Mayo" Zambada. "Both Mayo Zambada and Joaquin Guzman are permanent objectives because of the high danger they present to Mexico," said deputy security minister Patricio Patino.