Attorney General Eric Holder says the average number of mass shooting incidents has tripled in recent years -- calling the incidents "too frequent tragedies."
Speaking at the International Association of Chiefs of Police in Philadelphia on Monday, Holder said the U.S. experienced an average of five mass shootings every year between 2000 and 2008.
Since then, the annual average has tripled, Holder said. So far in 2013, there have been at least 12, he said.
"Even more troubling, these incidents seem to be getting more and more deadly," Holder told the crowd at the Pennsylvania Convention Center.
According to Justice Department figures on mass shootings, 404 people were shot and 207 people were killed from 2009 to 2012. From 2000 to 2008, 324 people were shot and 145 were killed.
Holder's comments came hours before another school shooting took place in Nevada on Monday afternoon. In that attack, a teacher and the shooter were killed and two students were hurt.
The attorney general said that in the past decade, the Justice Department has helped train 50,000 front-line officers, more than 7,000 on-scene commanders and over 3,000 local, state and federal agency heads on how to respond to active shooters.
"In order to prevent additional casualties, it is often patrol officers and not necessarily SWAT Teams who serve as the tip of the spear in responding to these incidents," he said. "The reality is that police don't always have the luxury of time to get their most highly-trained, best group of officers on the scene."
Holder added that all officers must have the most up-to-date training and equipment to deal with such incidents.
To disrupt planned shootings and other attacks, the FBI's Behavioral Threat Assessment Center works every day with local police and other levels law enforcement to assess people who may be contemplating violence.
Since 2011, the center has reported hundreds of successful disruptions, including an anticipated 150 this year alone, Holder said.