Federal firearms agents investigating gun traffickers were sidelined by their superiors in the "Fast and Furious" operation tracking guns to Mexican drug cartels, the agents testified in a Congressional hearing.

The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) agents told the House Oversight and Government Reform committee they were expressly told by supervisors not to "intervene and interdict" the loads of guns, reports FOX News.

Phoenix ATF agents Peter Forcelli and John Dodson told the committee they were repeatedly shut down, when they questioned their superiors.

"We weren't giving guns to people who were hunting bears. We were giving guns to people who were killing people," Forcelli told the committee, according to the Los Angeles Times.

Fast and Furious was part of Project Gunrunner, an ATF operation aimed at tracking the flow of guns to criminal groups in Mexico. Since it began in 2006, Gunrunner is credited with the seizure of more than 10,000 firearms and the arrests of more than 800 suspects.

In 2009, ATF's Phoenix office began Fast and Furious, in which agents monitored but did not disrupt the sale of guns from American dealers to suspected "straw purchasers," who obtain guns for criminal organizations.

About 2,000 to 2,500 weapons were sold in this way, reports the New York Times.

The ATF came under increasing scrutiny earlier this year, when several of these weapons were traced to the suspects who ambushed Border Patrol Agent Brian Terry and Immigration and Customs Enforcement Special Agent Jaime Zapata.

A AK-47 variant legally sold by a Dallas-Fort Worth firearms dealer was transported to the Los Zetas cartel operators who used it to attack special agent Jaime Zapata and Victor Avila Jr. Agent Zapata was killed during the Feb. 15 ambush.

In March, Homeland Security Chief Janet Napolitano told U.S. senators conducting Judiciary Committee hearings that she was not aware of the possible involvement of an ICE agent in the ATF operation.

By Paul Clinton

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