Less than half of the United States' porous southwest border with Mexico is under the operational control of the U.S. Border Patrol, according to a government watchdog.
The study by the Government Accountability Office said that the Border Patrol had achieved "varying levels of operational control" over just 873 miles, or 44 percent, of the nearly 2,000-mile border by the end of last year.
The report found that the number of miles under operational control increased an average of 126 miles per year from 2005 through 2010.
The GAO, which is the investigative arm of the U.S. Congress, noted that only 129 of those miles, or 15 percent, were classified as "controlled" -- the highest level for detecting and arresting intruders.
President Barack Obama's administration has been under intense pressure to beef up security on the southwest border to prevent raging drug cartel violence spilling over from Mexico and to stem an influx of illegal immigrants.
Of the nine Border Patrol sectors along the southwest border, only Yuma, in far western Arizona, had achieved complete operational control along its stretch of the border. The remaining sectors noted between 11 and 86 percent of their area under operational control .
The "Border Patrol attributed the uneven progress across sectors to multiple factors, including prioritizing resource deployment to sectors deemed to have greater risk from illegal activity," the report said.
Of the 1,120 miles of the border where operational control had not been achieved, around two-thirds were classified as "monitored," meaning that the Border Patrol had a high probability of detecting intrusions, although their ability to respond depended on the available resources.
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