Mesa County Sheriff / AP file A Draganflyer X6 drone is seen in a photo from the Mesa County Sheriff's Office in Colorado.

SEATTLE - A plan by Seattle police to send aloft miniature robot drones equipped with stealth spy cameras has been grounded, following heated criticism of the project by residents concerned about privacy rights, the mayor says.

Seattle Mayor Mike McGinn said Thursday that he and Police Chief John Diaz decided to cancel the use of two unmanned helicopters to better focus on maintaining the public's trust.

The miniature helicopters, known as Draganflyer X6 drones, weigh 3.5 lbs and are equipped to carry video, still and night-vision cameras. In Seattle, they would have been used to search for missing persons and in certain criminal investigations, police said.

The aircraft would not carry weapons but the use of drones for even mundane tasks raises ire among some because of the association of pilotless crafts with covert U.S. missile strikes in places such as Pakistan and Yemen.

Plans by a number of U.S. law enforcement agencies to use drones represent a new and controversial frontier for the technology.

A recent push for unmanned police aircraft was driven by U.S. Department of Homeland Security grants, including $80,000 used by Seattle to buy the eye-in-the-sky choppers in 2010.

"We agreed that it was time to end the unmanned aerial vehicle program, so that SPD can focus its resources on public safety and the community building work that is the department's priority," McGinn said in a statement.

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The drones, which could only remain aloft for 15 minutes before their batteries ran out, will be returned to the vendor, McGinn said.

Police in Florida's Miami-Dade County and Houston are among the law enforcement departments that have acquired aerial drones. Actual U.S. domestic use of police drone surveillance aircraft remains limited.

Colorado's Mesa County Sheriff's Department has operated two small drones since 2010, mainly to create three-dimensional images of crime scenes.

During a public hearing in Seattle on Wednesday, opponents of the drone program and the American Civil Liberties Union of Washington voiced concerns.

"Drones give law enforcement agencies unprecedented abilities to engage in surveillance and intrude on people's privacy," Doug Honig, spokesman for ACLU of Washington, said in an email to Reuters.

At another Seattle public meeting held in October to discuss the drone proposal, residents erupted into yelling and angry chants of "No drones!"