BALDWIN PARK, Calif. (NewsNation Now) — A fire inside an official Los Angeles County ballot drop box is being investigated as arson and has been reported to the FBI, authorities said Monday.

The fire was reported Sunday night in a curbside secured ballot box outside a library in suburban Baldwin Park, east of Los Angeles.

Firefighters put out the fire, cut open the box and pulled out envelopes, some charred. Arson investigators are handling the probe, according to police. Officials have not announced any arrests reported NewsNation affiliate KTLA.

The county registrar-recorder’s office said the items were being reviewed “to determine the appropriate notifications to voters whose ballots may have been impacted and will ensure they can exercise their fundamental right to vote.”

Ballots were last collected from the box shortly after 10 a.m. Saturday. Voters who dropped off ballots after that time were asked to call the registrar-recorder.

“The arson of an official ballot drop box by the Baldwin Park Library in the First District has all the signs of an attempt to disenfranchise voters and call into question the security of our elections,” said L.A. County Supervisor Hilda Solis in a statement. “Tampering, or attempts to tamper, with our democracy will not be tolerated.”

The frequency of ballot pickups at all boxes was being increased immediately.

Janice Hahn, also a member of the county Board of Supervisors, said the fire was reprehensible.

“Burning ballots is not just vandalism, it is an attack on our democracy and on our residents’ right to vote,” she said. “Whoever did this must be found and prosecuted to the fullest extent of the law.”

NewsNation Now affiliate KTLA’s Kristina Bravo, Carlos Saucedo and Nancy Fontan contributed to this report. The Associated Press contributed to this report.