Approximately 100 letters containing a white powder have been received by state legislators and public officials across Kansas, officials said, setting off an investigation that includes state and federal agencies.

Preliminary tests on a small sample of the letters show "the substance is presumptively negative for common biological agents of concern," the Kansas Bureau of Investigation said Sunday.

"Further and more complete testing will be conducted on this sample, as well as on additional letters that have been collected, in an effort to determine the components of the substance," the bureau said.

No injuries have been reported, the KBI and a spokesperson for state House Speaker Daniel Hawkins said. Hawkins, a Republican, received one of the letters, his spokesperson Carrie Rahfaldt said.

Republican state Rep. Stephen Owens said he also received one of the letters and believes the others who received them are fellow Republicans.

The letter read, in part, "it's important not to choke on your ambition," and was signed "your secret despirer," according to a copy Owens shared with CNN.

The FBI is assisting the KBI and other state agencies with the investigation, which comes amid political battles between the state's Republican-led House and Senate and Democratic Gov. Laura Kelly.

The state legislature has voted to override nine of Kelly's vetoes this year, according to Owens, including one on a bill banning transgender female athletes from competing on sports teams consistent with their gender from kindergarten through college, and another bill dubbed the "Women's Bill of Rights" that defines an individual's sex only as the one assigned at birth.

"There's a question whether maybe it's related to some of those vetoes that we overrode," Owens said of the letters. "It's really terrifying to think that because of someone's political beliefs that they can be a target," he said.

Investigators have encouraged people to "remain vigilant" while handling mail.

Owens opened the letter thinking it was from one of his constituents because the return address on the envelope was for a church in his district, he said.

"It was very deliberate, very intentional to get us to open the letters," Owens said.

Despite the letters, Owens says his resolve and that of his Republican colleagues will not waver.

"Violence and acts of violence and threats do absolutely nothing, nothing to change one's perspective. As a matter of fact, that strengthens the resolve of myself and my colleagues and of our party to continue the work that we're doing," Owens said.

"We are very appreciative of KBI Director (Tony) Mattivi, the agents of the KBI, local law enforcement and fire departments, the KS National Guard, KDHE, the FBI, the Office of the State Fire Marshall, and everyone else who was involved in the massive process of retrieving these envelopes and ensuring the safety of our members," Rahfaldt, the House speaker's spokesperson, said.