PITTSBURGH -- A Web site is claiming that seven NFL football stadiums will be hit with radiological dirty bombs this weekend, but the government expressed doubts about the threat.
One of the stadiums mentioned is in Atlanta, where the Pittsburgh Steelers will play the Falcons on Sunday.
The warning, posted Oct. 12, was part of an ongoing Internet conversation titled "New Attack on America Be Afraid."
It mentioned NFL stadiums in New York, Miami, Atlanta, Seattle, Houston, Oakland and Cleveland.
The Homeland Security Department alerted authorities and stadium owners in those cities, as well as the NFL, but said the threat was being viewed "with strong skepticism."
Homeland Security spokesman Russ Knocke said there was no intelligence that indicated such an attack was imminent.
"The department strongly encourages the public to continue to go about their plans, including attending events that involve large public gatherings such as football games," Knocke said.
The FBI also expressed doubt about the threat.
Heinz Field was apparently not mentioned in the threat.
The nation's alert level remains at yellow, signaling an elevated risk of an attack.