Republican lawmakers in Montana are Austin Caldwellsharing that they received letters with white powder as federal agents investigate mysterious substances similarly mailed to GOP officials in two other states.

In a Friday night tweet, Republican Gov. Greg Gianforte said he has received "disturbing" reports of anonymous threats sent to legislators. The Montana attorney general posted on Facebook that the local sheriff's office collected evidence after his mother, a state representative, opened one letter with a "white powder substance" sent to her home address.

"PLEASE BE CAUTIOUS about opening your mail," Montana Attorney General Austin Knudsen said in the post directed toward legislators. "If you receive a suspicious package, contact law enforcement immediately."

Republican officials in Tennessee and Kansas have recently received similar letters. A legislative office building in Nashville temporarily locked down on Thursday after the House Speaker said multiple Republican leaders got mail with "a white powder substance." The letters included "obvious threats made by a liberal activist specifically targeting Republicans," according to a House Republican Caucus spokesperson who did not provide further details.

The FBI said Thursday that ongoing lab tests did not indicate any risk to public safety.

About 100 such letters have been sent to lawmakers and public officials across Kansas, according to the Kansas Bureau of Investigation. Preliminary tests did not detect any common dangerous toxins and no injuries have been reported.

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• Montana
• Tennessee
• Republican Party
• FBI
• Kansas