An avowed anti-abortionist on the FBI's Ten Most Wanted list was named Thursday as the chief suspect in a series of anthrax threats sent to abortion clinics throughout the U.S.

Attorney General John Ashcroft urged all Americans to help the FBI track down "self-described anti-abortion warrior" Clayton Lee Waagner, who has been on the FBI's "Top Ten" list since September.

Ashcroft said the FBI had obtained information over the Thanksgiving holiday indicating Waagner, 44, had claimed responsibility for sending more than 280 letters to abortion clinics across the United States.

The FBI considers Waagner "extremely dangerous. He has survival skills and may be heavily armed," Assistant FBI Director Rueben Garcia said.

Family-planning clinics in at least 12 states, including Tennessee, have received letters containing anthrax threats, according to officials of feminist and abortion-rights organizations.

The Feminist Majority Foundation said more than 450 clinics and advocacy organizations received letters in envelopes carrying white powder and letters signed by "the Army of God." Clinics in Nashville, Knoxville and Oak Ridge were among those that received the letters, all postmarked from Atlanta.

None of the powder sent to the clinics has tested positive for anthrax.

Waagner escaped in February from a Clinton, Ill., jail where he was awaiting sentencing on federal firearms and auto theft convictions. He also is being sought for a Pennsylvania bank robbery, firearms violations in Tennessee and a carjacking in Mississippi.

Police said that on Sept. 7, Waagner abandoned a car on a highway in Memphis after colliding with a tractor-trailer. A pipe bomb was found in the car, along with anti-abortion literature and weapons.

Hours later, a man believed to be Waagner committed a carjacking in Tunica, Miss., 40 miles southwest of Memphis, authorities said. A casino there was evacuated after a tip that he was there.

He had been arrested in September 1999 after entering Illinois with his wife and eight children in a stolen Winnebago, which had four stolen handguns under the driver's seat, authorities said.

During his trial, Waagner testified that he had watched abortion clinics for months, stocking up weapons after God asked him to "be my warrior" and kill doctors who provide abortions.

In June, abortion clinics were warned after someone purporting to be Waagner posted an Internet message threatening to kill employees of abortion providers.

That same month, a federal grand jury charged Waagner with robbing a bank just outside Harrisburg, Pa., in May.

The FBI is offering a reward of $50,000 for information leading to Waagner's arrest.

The Associated Press contributed to this report.