A former POW resigned as a volunteer to President Bush's (search) re-election campaign Saturday after it was learned that he appeared in an anti-John Kerry ad sponsored by the Swift Boat Veterans for Truth (search).

The Bush campaign has claimed no connection with the group which has led an attack on Kerry, the Democratic presidential candidate, questioning his war record in Vietnam and criticizing his testimony at a congressional hearing in 1971 in which Kerry alleged U.S. troops committed atrocities.

Retired Air Force Col. Ken Cordier (search), resigned as a member of the Bush campaign's veterans' steering committee after it was learned that he appeared with other former POWs in a 30-second ad, produced by the Swift Boat group, criticizing Kerry's congressional testimony.

"Col. Cordier did not inform the campaign of his involvement in the advertisement," the Bush campaign said in a statement. "Because of his involvement (with the group) Col. Cordier will no longer participate as a volunteer for Bush-Cheney '04."

Cordier spent six years in a North Vietnamese prisoner of war camp.

The White House and the Bush campaign have denied any direct connection with Swift Boat Veterans for Truth, which is funded in part by a top GOP donor in Texas.

"The president has made it repeatedly clear that he wants to see an end to all" advertising from outside groups, said Brian Jones, a Bush campaign spokesman.

Kerry, at a fundraiser in East Hampton, N.Y., on Saturday called on Bush to "stand up and stop" what he called personal attacks on him over his combat record in Vietnam by the Swift Boat group.

"The president needs to stand up and stop that. The president needs to have the courage to talk about it," said Kerry.