The Bush administration said Tuesday the people who beheaded American hostage Nick Berg (search) in Iraq are enemies of freedom who will be hunted down and brought to justice.

"Our thoughts and prayers are with his family," White House Press Secretary Scott McClellan said of Berg.

"It shows the true nature of the enemies of freedom. They have no regard for the lives of innocent men, women and children. We will pursue those who are responsible and bring them to justice."

McClellan was in Arkansas with President Bush on a campaign visit to spotlight Bush's education policies. The president spoke at a junior high school before news broke of the killing of Berg, 26, of West Chester, Pa.

An apparent videotape of Berg's beheading was aired on a Web site known to have ties with Usama bin Laden's Al Qaeda (search) network. The tape also included threats against Bush and Pakistan's president, Gen. Pervez Musharraf (search).

In Washington, word of the beheading reached the Senate as the Armed Services Committee was holding a hearing into the abuse of Iraqis at the Abu Ghraib prison (search).

"Senators ... are in a virtual state of shock about the beheading," said Sen. John Warner, R-Va., recalling earlier concerns that the prisoner abuse could lead to retaliation against Americans.

Gen. Ronald L. Burgess told Warner "there has been an increase" in threats in the days since the prisoner abuse became known through the publication of photographs.