Mora was to be transported to Mexico City and handed over to the federal prosecutors' office for interrogation.

The statement did not provide further details of Mora's suspected role in the killing.

A news conference where Mora was to be presented to journalists in Mexico City was canceled shortly before it was supposed to begin Sunday evening.

U.S. Immigration and Customs Enforcement (ICE) agent Jaime Zapata died and his partner was wounded when they were ambushed in broad daylight on a major highway outside of the city of San Luis Potosi earlier this month by alleged drug gang members.

It was one of the worst attacks on U.S. law enforcement personnel in Mexico in more than a decade.

Mexico's federal prosecutors' office believes the attack was due to a mistaken identity, but it has come under heavy diplomatic pressure from Washington to capture Zapata's killers.

Security forces have already arrested six men, four women and a minor in connection with the attack, all of whom are allegedly linked to the Zetas.

Nine of those arrested were ordered held in prison for 40 days on Sunday by a Mexican judge to allow prosecutors more time to collect evidence against the suspects before they were charged.

The Zetas, formed by renegade Mexican special forces soldiers who deserted to become the armed wing of the Gulf Cartel, have grown in power. They turned on their former masters last year to battle for control of lucrative drug smuggling routes in northern Mexico.

Escalating drug violence in Mexico, a top U.S. trade partner, has caused alarm in Washington, which is providing $1.3 billion in funding and training to help battle the local cartels.

Mexican President Felipe Calderon has made crushing the cartels a top priority of his government and has sought to enhance cooperation with U.S. authorities in his fight.

More than 34,000 deaths are blamed on drug violence since Calderon took office in late 2006 and launched his army led campaign against the gangs.

**Reporting by Robert Campbell; Editing by Cynthia Osterman and Paul Simao