ATLANTA (AP) - Federal agents are investigating two fires in the past week at women's clinics in metro Atlanta, authorities said.

The fires happened on Sunday in Gwinnett County and Wednesday at an "abortion services" clinic in Cobb County that was the site of anti-abortion protests in the past.

"We're investigating the possibility of a link between the two, but we haven't come to a conclusion yet," said Richard Coes, a spokesman for the Bureau of Alcohol, Tobacco, Firearms and Explosives. He declined further comment on Thursday on the status of the investigation.

The Sunday blaze took place at the Atlanta Gynecology and Obstetrics Gwinnett office in Lilburn, and fire investigators described it as suspicious. A K-9 indicated that an "incendiary substance" was present at the Lilburn fire scene, and lab tests are under way, FBI officials told The Gwinnett Daily Post.

On Wednesday, more than 20 firefighters rushed to put out the flames at a clinic about 20 miles away in Marietta. No one was hurt in the fire but there were about 20 employees and several patients inside when it started, said Cobb County Fire spokeswoman Denell Boyd.

An employee said she saw two men climb the stairs to the third floor of the building and then quickly descend before a fire started on that floor.

"One of our employees started smelling the smoke, they heard a bunch of racket back and forth and then they smelled it," Angela Buckner, a nurse who works in the clinic, told The Atlanta Journal-Constitution.

Cobb County's fire department arson unit is investigating the blaze with help from federal agencies, said Sgt. Dana Pierce, the county's police spokesman.

The two fires, along with several burglaries that struck women's clinics in recent months, have raised concerns that the clinics are being targeted by vigilantes.

The physicians who were victims of the burglaries and Sunday's fire did not perform abortions but they had all visited the statehouse this session to discuss the impact of abortion-related legislation, said Dr. David Byck, president of the Georgia Obstetrical and Gynecological Society.

"We are concerned that each of these physicians spoke with lawmakers during the session and that each then became targets of felony crimes," Byck said in a statement.