SAN'A, Yemen - The cleric preached in his tiny Yemeni village about the evils of al-Qaeda, warning residents to stay away from the group's fighters. The talk worried residents, who feared it would bring retaliation from the extremists, and even the cleric's father wanted him to stop.

In the end it wasn't al-Qaeda that killed Sheikh Salem Ahmed bin Ali Jaber - but a U.S. drone.

Yemeni security officials confirmed that three extremists - along with Salem and his cousin, who were going to meet them apparently to discuss his sermons - were killed in a drone strike in August.

In its covert fight against al-Qaeda in Yemen, the United States has dramatically stepped up its use of drone strikes the last year, scoring successes against one of the most active branches of the terror network. With more than 40 strikes reported in 2012 and nine so far this year, Yemen has become the second-biggest front in American drone warfare, after Pakistan.

But the escalation has meant more civilians getting caught in the cross fire.

Civilian deaths are breeding resentments, sometimes undermining U.S. efforts to turn the public against extremists.

Several dozen activists protested Monday near the U.S. Embassy in San'a, denouncing the strikes.

At a Senate Judiciary Committee hearing in Washington last week on the drone program, Farea al-Muslimi, a Yemeni whose village had been struck only days earlier, told the senators that drones were "harming efforts to win hearts and minds," saying drones were now "the face of America" to many Yemenis.