May 11 (Bloomberg) -- The U.S. will track down and punish those who beheaded an American hostage in Iraq, White House spokesman Scott McClellan said after an Islamic Web site said the killing was in response to U.S. abuse of Iraqi prisoners.

The American, who was bound and wearing an orange jumpsuit, identified himself on the video as Nick Berg from Philadelphia, a civilian U.S. contractor. His body was found on a highway overpass in Baghdad Saturday, the Associated Press said.

``This shows the true nature of the enemies of freedom,'' McClellan said in response to questions from reporters traveling with President George W. Bush from an education speech in Arkansas. ``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.''

Video of the killing by five men wearing headscarves was posted on an Islamic Web site. It said Berg, 26, was killed by an al-Qaeda-affiliated group to avenge the abuse of Iraqi detainees at Abu Ghraib prison, AP said.

Publication worldwide of photos showing smiling U.S. soldiers posing with naked and bound detainees at Iraq's Abu Ghraib prison have sparked probes in the U.S. Congress and criticism of the Bush administration's handling of the Iraq occupation.

Bush and Defense Secretary Donald Rumsfeld have apologized and Rumsfeld proposed offering compensation to Iraqi victims.

`Believed in the Cause'

The Web site on which the video of Berg's murder was posted is ``a mouthpiece for al-Qaeda and other terrorist groups,'' said Rita Katz, director of the SITE Institute, a Washington-based group that tracks terrorist organizations.

The video bore the title ``Abu Musab al-Zarqawi shown slaughtering an American,'' AP said.

The U.S. says Jordanian Zarqawi, believed to be operating in Iraq, is affiliated with the terrorist group al-Qaeda. He is wanted in connection with the murder of a U.S. aid official in Jordan.

Berg went to Iraq ``because he believed in the cause and he wanted to help the Iraqi people rebuild their infrastructure,'' said Walter Billings, president of Total Engine Service and Supply Co., for whom Berg worked as a contractor.

Billings said Berg had performed painting, repairs and troubleshooting for problems, among other engineering and maintenance tasks on radio towers as high as 900 feet tall outside Baltimore and Washington, for the company's Comm- Struction and Services division, based in Bel Air, Maryland.

Physically Fit

``He was physically fit and he had a zest for adventure,'' Billings said. ``You don't climb those towers and hang by a harness unless you've got a spirit of adventure. It's not every Tom, Dick and Harry who goes into that business.''

Berg had tried to persuade Billings and his partner to join him in Iraq ``but we decided against it, given the climate that was developing there,'' Billings said.

Berg traveled to Kenya to help install radio and television towers about two or three years ago, Billings said.

The Council on American-Islamic Relations, based in Washington, decried Berg's killing.

``We condemn this cold-blooded murder and repudiate all those who commit such acts of mindless violence in the name of religion,'' the group said in a statement. ``We call on people of all faiths and cultures to work together for peace and reconciliation, not war and destruction.''

Kerry `Horrified'

Democratic presidential candidate John Kerry said he was ``horrified and deeply saddened by the senseless murder of Nicholas Berg.''

``The terrorists who committed this atrocity will not prevail, and America stands together against them,'' Kerry, a four-term senator from Massachusetts, said in a statement.

Kerry, 60, also said prisoner abuse in Iraq by U.S. troops stemmed from an ``arrogance'' of policy under Bush.

``It's not just a few privates and corporals, sergeants,'' Kerry told a fund-raising event in Louisville, Kentucky. ``This is something that comes out of attitude about the rights of prisoners of war. It is an attitude that comes out of how we view the prisoners. It is an attitude that comes out of an overall arrogance and policy.''

Bush's re-election campaign spokesman called Kerry's comments about Bush's military policies ``appalling'' and ``a new low.''

``John Kerry never misses an opportunity to play politics with the war on terror,'' campaign spokesman Scott Stanzel said in an e-mail.

To contact the reporter on this story: Holly Rosenkrantz in Washington at hrosenkrantz@bloomberg.net

Last Updated: May 11, 2004 20:14 EDT