WASHINGTON - Sophisticated surveillance aircraft will be deployed along the nation's southwestern border in the coming months to peer as much as 6 miles into Mexico to spot smugglers, drug traffickers and undocumented immigrants and give armed U.S. Border Patrol agents an edge intercepting intruders as they cross into the United States, Obama administration officials said Tuesday.

A Predator drone takes off on a U.S. Customs and Border Protection mission from Fort Huachuca, Ariz. The Federal Aviation Administration had been asked to issue flying rights for a range of pilotless planes to carry out civilian and law-enforcement functions but was hesitant to act for safety reasons. Six years later, there are now drones patrolling most of the U.S.-Mexico border, from Yuma, Ariz., to Brownsville, Tex. (Ross D. Franklin / AP) The plan to operate crewed, high-tech aircraft with "over the horizon" technology came to light as the Pentagon and Department of Homeland Security announced the end of the 18-month-old deployment of 1,200 National Guard ground troops who have been helping the U.S. Border Patrol spot illegal border crossers.

The winding down of the ground operation over the next two months stems from growing concerns over the cost and effectiveness of the $10 million-a-month National Guard effort that has provided reassurance along the border and political cover for politicians in Washington but has had limited impact on arrests and drug seizures.

By using unmanned drones, which already are active in the area, and aircraft operated by the "citizen soldiers" of the National Guard, the Obama administration avoids diplomatic strains that might arise with Mexico if U.S. military surveillance aircraft flown by active-duty armed forces' pilots were used along the common border.

Ricardo Alday, spokesman for Mexico's Embassy in Washington, said the Mexican government would have no objection to the cross-border surveillance.

Under the plan unveiled Tuesday, airborne spotters aboard Air National Guard aircraft will relay the routes of prospective border crossers to U.S. Border Patrol agents, helping U.S. law enforcement "reduce enforcement response time (and) enabling Border Patrol officers to quickly move from one location to another on short notice to meet emerging threats of illegal activity or incursion," officials said in a statement.