Washington DC - The sibling ex-leaders of Mexico's Zetas cartel were arraigned on Friday in the US on charges including drug trafficking, firearm possession, and money laundering, the US Department of Justice said.

Brothers Miguel and Omar Trevino Morales – aliases "Z-40" and "Z-42" – led one of Mexico's most powerful and feared organized crime groups until its collapse.

They were among the 29 drug suspects that Mexico extradited to the US last month, as it faces mounting pressure from President Donald Trump to tackle drug smuggling.

The brothers were arraigned in Washington "on charges of engaging in a continuing criminal enterprise that involved multiple murder conspiracies," the Department of Justice said in a statement.

Their other charges included "conspiring to manufacture and distribute large quantities of cocaine and marijuana destined for the United States, using firearms – including a machine gun – during and in relation to drug trafficking crimes, and conspiring to launder monetary instruments."

Zetas was founded by deserters from the Mexican special forces known for their brutality.

Miguel Trevino Morales led the Zetas until Mexican authorities arrested him in 2013, when his brother Omar took over until his arrest in 2015, the Department of Justice said.

"After their arrests, the defendants allegedly renamed Los Zetas to Cartel del Noreste (CDN) and continued to control the cartel while incarcerated in Mexico," it added.

The State Department said last month it had designated CDN as a "foreign terrorist organization."

Washington accuses the two brothers of being "personally responsible" for committing dozens of murders and for directing killings, kidnappings, and torture.

Both pleaded not guilty on Friday, and face the possibility of the death sentence if convicted, according to reporters at the hearing.