CHICAGO — The US government Wednesday denied it was hampering the case of an alleged senior member of the Sinaloa cartel by refusing to hand over top secret data on the American fight against drug-trafficking.

Jesus Vicente Zambada-Niebla, son of one of Mexico's most-wanted drug kingpins, is on trial in Chicago for trafficking huge amounts of heroin and cocaine and could face life if convicted.

But he has contended since his 2009 arrest and 2010 extradition from Mexico that he is covered by an immunity deal with the United States under which the cartel's top leadership supplied information on rival gangs.

His lawyers say under the deal with the US Drug Enforcement Agency, Zambada and his cartel members were offered protection from prosecution, and argue the charges should be dropped.

Although the war on drug-trafficking particularly over the joint US-Mexico border is a top concern of President Barack Obama's administration, prosecutors staunchly deny any such deal was ever struck.

The trial is due to start in February, but in a pre-trial hearing Wednesday, Zambada's defense team told Judge Ruben Castillo the government has failed to hand over documents vital to their case.

Government lawyers argue the documents contain classified -- potentially volatile -- information and cannot be made available even to the defense team for more than seven days.

They cited regulations set out under the Classified Information Procedures Act (CIPA), arguing measures needed to be taken to ensure none of the classified material ever becomes public.

Prosecutors cited "significant security concerns" regarding the documents wanted by the defense to fight the case for Zambada, son of Sinaloa leader Ismael "El Mayo" Zambada.

"The threat here is not just to the two witnesses in this case, but to their families," said assistant US attorney Thomas Shakeshaft. "That's a genuine concern -- the ability to influence testimony."

Judge Castillo said while he was not going to "make light of government security concerns," he felt such a short time frame was "inherently unfair" and adjourned the hearing until October 27.

A Justice Department report released earlier this month showed the Sinaloa cartel and its powerful Mexican rivals have become the top suppliers of illegal narcotics into the United States.

Zambada's claims have thrown a spotlight on the shadowy world of narcotics agents and the violent, dangerous fight to stem the drug trade.

"These kinds of deals are the bread and butter of how you go about bringing down drug traffickers," said Shannon O'Neill from the Council on Foreign Relations.

"They don't want to talk about this on the record -- it doesn't look pretty and it's not the kind of thing you want to imagine your police forces or law enforcement officers doing."

Mexican authorities claim more than 35,000 lives have been lost since President Felipe Calderon launched an offensive against drug cartels in late 2006. Media reports put the total toll at nearer 41,000, including criminals, security forces and civilians.