U.S. Customs and Border Protection identified the vehicles as belonging to a team normally stationed in South Florida that had recently been assigned out of state, Earley said. The agents believed they could vote at the Northeast Library site, near U.S. Highway 319, which is the last voting location along the highway before it exits Florida.

Earley said he accepted that explanation and considered the incident isolated. He said it was consistent with assurances election officials had received that federal agents would not be stationed at polling places, and sought to reassure voters that in-person voting was safe.

The sighting came after election officials in two Florida counties reported federal agents at or near early voting locations. In Monroe County, Supervisor of Elections Sherri Hodies said she opened an investigation after reports of masked federal agents conducting a stop at a polling place in Key Largo. Earley and Hodies both filed formal complaints with the FBI.

Federal law generally bars armed federal agents from conducting activities in and around polling places, except when necessary to repel armed enemies of the United States. At a statewide conference this summer, the FBI told Florida elections supervisors there would be no immigration enforcement at polling places, amid rumors about possible enforcement activity during the midterm elections.

Florida early voting is scheduled to end Sunday, Nov. 1. The reports have put renewed attention on assurances that voters can cast ballots without intimidation or federal enforcement activity at polling sites.