KABUL, Afghanistan - The brutality of Taliban attacks in northwest Pakistan has cost the militants public support, the U.S. special envoy to the region said Saturday.

Richard Holbrooke, making his sixth trip to Afghanistan in the past year, said the ruthlessness of militants like Hakimullah Mehsud, the leader of the Pakistani Taliban, is beginning to "backfire" on the extremist network's operation in the Swat valley.

Holbrooke, who visited the Swat valley a few days ago, cited Swat's notorious Taliban leader Maulana Fazlullah whose radio broadcasts long spread fear among residents of the valley and Mehsud, the apparent target of a U.S. airstrike on Thursday.

"I feel that the extremists ... have overshot their mark," Holbrooke said. "I think that brutality with which they approach Swat has now backfired."

The death of Mehsud would be a victory for the United States and Pakistan in their fight against Islamist militants. Mehsud was seen on a recent video sitting cross-legged next to the Jordanian militant who killed seven CIA employees in a suicide attack in December in eastern Afghanistan. Mehsud's Tehrik-e-Taliban movement, which is linked to al Qaeda and the Taliban across the border in Afghanistan, has also claimed responsibility for scores of bloody suicide bombings in Pakistan in recent months against military, civilian and government targets.

It's not certain that Mehsud lived through the U.S. airstrike, but three Pakistani intelligence officials and four militants told The Associated Press that Mehsud was not among the dead.

"I've heard every conceivable version of what's happened to him, and I don't know," Holbrooke told reporters at the heavily secured U.S. Embassy in the Afghan capital of Kabul. "But if he's still alive, he's one of the worst people on earth -- one of the most vicious."

"I don't know what his status is. We've heard all the rumours, and we're just going to sit back and let it develop, but I do want to stress how strongly we feel about this man and that group."