BIRMINGHAM, Ala. (AP) _ Federal agents are investigating letters in which a group linked to anti-abortion terrorism claim responsibility for the bombing of a Birmingham abortion clinic that killed a security guard and injured a nurse, the FBI said Monday.

FBI spokesman Craig Dahle said the letters claim the ``Army of God'' was responsible for the nation's first fatal bombing of an abortion clinic, the same group that claimed to have bombed an Atlanta abortion clinic last year.

Dahle said he understood the letters were hand-written with block print and there were indications they were similar to communications sent claiming credit for the Atlanta clinic violence.

The Army of God is a name that has been circulating since the 1980s as a force for radical anti-abortion actions, including circulating a manual that contains information on how to make bombs. It's not clear who makes up the organization, although various anti-abortion activists have either been linked to it or claimed to be part of it over the years.

The letters surfaced Monday as federal agents continued to search for a North Carolina man whose truck was seen near the bombed clinic, and as funderal services were held for the slain clinic guard.

Dahle declined comment on a CNN report that the letters were sent to the Atlanta Journal-Constitution and the Reuters news service. He said only that the Birmingham FBI ``confirmed the existence'' of the communications, and would not comment on whether they had been intercepted by law enforcement authorities.

Donna Lorenz, deputy metro editor at The Atlanta Journal-Constitution, said the newsroom did not actually receive the letter. She said the FBI sent over a fax of the letter and that she did not know how the FBI got it.

Dahle said that while federal agents are investigating the material, it is ``too soon to say anything now'' as to the authenticity of it.

The claims by the Army of God came as workers prepared to enter the New Woman All Women Health Care clinic for the first time since the bombing and as hundreds of law officers gathered for the funeral of the policeman killed in the blast.

Some of the bomb-damaged windows at the clinic already had been replaced, the electricity was on and the telephones were working. Most of the bomb damage was to the clinic's exterior.

``We will be seeing patients on Thursday this week,'' said owner Diane Derzis. ``We'll work all night if we have to.''

She denied that women might be afraid to visit the clinic so soon after the fatal attack.

``This is the safest clinic in the U.S. right now,'' Ms. Derzis said as investigators prepared to leave the site, picked clean of bomb fragments and other evidence.

Ms. Derzis met with reporters outside the clinic a few hours before hundreds of police officers from Alabama and the Southeast gathered at the Homewood Church of Christ in a cold rain for the funeral of Birmingham police officer Robert Sanderson.

Sanderson, 34, became the first person to die in an abortion clinic bombing in the United States when a package detonated outside New Woman on Thursday. He was working off-duty as a security guard.

``When a police officer dies everyone suffers. We have to pull together,'' Birmingham police officer James Hickey said outside the funeral where scores of patrol cars were parked.

The clinic's head nurse and counselor, Emily Lyons, 41, was seriously injured. Her condition was upgraded from critical to serious, said University Hospital spokesman Hank Black.

No arrests have been made, and authorities are still looking for Eric Robert Rudolph, the North Carolina man sought as a witness in the bombing. A gray 1989 Nissan pickup truck registered to Rudolph was seen near the clinic following the explosion, authorities said.

While agents were still working on the case, many took time to go to Sanderson's funeral, said FBI spokesman Craig Dahle.

``It's a time to reflect,'' he said.

Abortion-rights supporters from around the country traveled to Birmingham to show their support for the New Woman clinic and to help repair the damage.

``The only way terrorists will win is if we fail to reopen clinics after they have been hit,'' said Kathy Spillar, national director of the Feminist Majority Foundation. ``We will not be intimidated.''