The chief of the U.S. Border Patrol defended his agency Wednesday against criticism that agents are too aggressive in using deadly force, telling the audience at a conference that he takes the issue very seriously.

Chief Michael Fisher said there's been a mischaracterization that his employees "indiscriminately" open fire on immigrants.

He noted that, though highly-trained, at the end of the day, border agents are still human beings who experience fear and apprehension like anyone else.

"If you are like me, there's nothing more terrifying than fighting for your life when you're alone with no communication, and the thought for a split second that you may never get home at the end of that shift to see your wife and son again," Fisher said.

"The only thing that is equal to the ripple of fear is thinking of having to use deadly force against another human being," he added.

Immigrant rights groups accuse Border Patrol agents of being trigger-happy in responding to would-be crossers who throw rocks at them from the Mexican side of the border. The agency has maintained that often people throw rocks to distract agents from smugglers sneaking drugs into the U.S.

In a significant directive quietly issued earlier this month, Fisher reiterated that agents shouldn't fire their weapons unless absolutely necessary. The "level of force applied must reflect the totality of the circumstances surrounding each situation,'' he said.

Fisher has said that agents have been assaulted with rocks more than 1,700 times since 2010. Agents have used deadly force in 43 of those times, resulting in 10 deaths.

Fisher said that the use of a force is a difficult topic but there are standards and policies that address it.

"We want the independent investigators to come and to assess whether that agent exercised good judgment in the application of that force,'' he said.

Fisher said he was proud of the work his agents do.

He also delved into figures that show the recidivism rate for illegal border crossings has significantly decreased in the last decade. That rate dropped from a 28 to 39 percent between 2006 and 2009 to about 10 percent now, Fisher said.

Agents made 420,789 apprehensions in the 2013 fiscal year that ended in September. That's a 16 percent increase from the prior year but still a deep decrease from levels in 2008.

More than 98 percent of those arrests were made on the Southwest border, particularly in Texas. Officials have said the increase is caused by an influx of migrants from Central America who have been arrested in south Texas.

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