The mass killing at a Denver-area theater screening of the latest Batman thriller, "The Dark Knight Rises," has put metro Atlanta authorities on alert, and at least one leading chain, AMC, is banning costumes from its locations.

"The Dark Knight Rises" is opening this weekend at 4,404 theaters in metro Atlanta and the rest of the U.S. and Canada.

"At this time, we are not aware of any ongoing or immediate threats to movie theaters," Atlanta Police Chief George Turner said Friday. "We are in constant contact with the FBI, and if that changes we would immediately act to notify theater owners and patrons and provide extra security. "

Turner said the APD has a working relationship with private security agencies and "will certainly assist them with any requests for extra security or patrols to ensure the safety and peace-of-mind of their patrons."

Police say a former medical student in a gas mask, identified as 24-year-old James Holmes, barged into a crowded Denver-area theater during a midnight showing of the Batman movie, hurled a gas canister and then opened fire, killing at least 12 people and wounding at least 59 others. It is one of the deadliest mass shootings in recent U.S. history.

Cobb County police spokesman Sgt. Dana Pierce said theaters in the area generally have a police officer or sheriff's deputy working to maintain security. "They will be working with a heightened awareness of what happened in Colorado and be on the lookout for any suspicious activity or potential copycats," Pierce said.

Authorities in Gwinnett and DeKalb also are working with theaters to ensure locations are secure.

The shooting occurred at a Century 16 Theater in the Denver suburb of Aurora. The theater is owned by Cinemark Century Theatres, which has few locations in metro Atlanta. Efforts were being made to reach Cinemark for comment.

AMC spokesman Ryan Noonan said in a statement to The Atlanta Journal-Constitution that the theater chain, which has multiple locations showing "Dark Knight" in metro Atlanta, is working with local authorities to beef up security.

AMC, the second-largest movie chain in North America behind Regal, said it will no longer allow guests to bring costumes, facial masks or fake weapons into theaters. There were unconfirmed reports that Holmes dyed his hair to look like the Joker, a Batman villain in the movie.

AMC said it will provide refunds for tickets or ticket exchanges in light of the new costume policy. Movie schedules, however, will not change.

"Under the circumstances, we are reaching out to all of our theatres to review our safety and security procedures," Noonan said. "Being a safe place in the community for all our guests is a top priority at AMC and we take that responsibility very seriously."

Regal Entertainment spokesman Russ Nunley also said security and safety was a top priority at the largest movie theater chain. "As is our custom, we will continue to monitor the situation and adjust our security needs as necessary," Nunley told the AJC.

Cynthia Hutchinson, a Carmike Cinema manager in Atlanta, said her theater had a midnight screening of the new Batman movie and it attracted about 400 patrons.

"We already employ several off-duty officers," Hutchinson said Friday. "We actually have them every day but on weekends we have increased security."

Hutchinson said she didn't hear about the shootings in Denver until Friday morning. "It's really sad. It kind of hits close to home, and when you think about it, it could happen to anyone anywhere."

Metro Atlanta police aren't the only ones on heightened alert.

The New York City Police Department is beefing up patrols at theaters showing the Batman movie "as a precaution against copycats and to raise the comfort levels among movie patrons," according to a statement by Police Commissioner Ray Kelly.

Officers from the Los Angeles Police Department were sent to check on theaters. "There's nothing that suggests that there's anything sinister planned beyond what happened in Colorado," Sgt. Enrique Mendoza told the Los Angeles Times. "What happened in Colorado appears to be an anomaly, an isolated incident."