MONTGOMERY — Letters containing white powder that were sent to seven governors all had Dallas postmarks, the FBI said Tuesday.

Government operations were disrupted Monday when workers in Alabama, Michigan, Minnesota, Mississippi, Missouri, Montana and Rhode Island opened the letters and discovered white powder.

Tests showed the powder wasn’t dangerous.

In Alabama, the Department of Public Safety said Tuesday the letter received at its state Capitol contained a harmless food substance. In Missouri, a chemical analysis by the state health lab found the powder appeared to be bleached flour, spokeswoman Nanci Gonder said Tuesday.

FBI spokesman Rich Kolko in Washington, D.C., said the Dallas FBI office is investigating and warned other states to be on the lookout for similar letters.

The FBI declined to say if the letters were specifically addressed to each governor or written to a generic “governor’s office” address.

Alabama’s public safety director, Christopher Murphy, said the letter received in Montgomery did not specifically target Gov. Bob Riley but declined to elaborate on what it said.

“That is a point of relief,” Murphy said.

The letters forced the evacuation of the Capitol in Helena, Mont., and the closing of a major street in downtown Montgomery for several hours. Hundreds of law enforcement and public safety employees were involved between the seven states.

“Just because it’s a hoax, doesn’t mean it’s not a crime,” Kolko said.

FBI spokeswoman Angela Toban said the drain on resources was enormous.

– Associated Press writers Chris Blank and David A. Lieb in Jefferson City, Mo., contributed to this report.