Fentress County Sheriff Chucky Cravens resigned Friday amid a state and federal investigation.

In a letter from his attorney, Cravens said "I deeply regret the circumstances that have led to my resignation." 

The FBI and TBI were at the Fentress County Sheriff's Department Tuesday as part of their investigation. FBI Assistant Special Agent Matthew Espenshade said they were looking into "allegation of impropriety."

Federal agents seized two county trucks as part of their investigation, one of them was used by Cravens.

No charges have been filed.

"During the past week, I have been in constant contact directly with the FBI regarding this pending case against Sheriff Cravens," said Fentress County Sheriff's Office Chief Deputy Gary Ledbetter in a news release. "I have been authorized to share with you that the primary focus of the FBI investigation was related only to the actions of Sheriff Cravens and NOT the Fentress County Sheriff's Office as a whole."

David Boling, a spokesperson for the U.S. Attorney's Office, said there was no update on the investigation Friday night. 

MORE: Federal investigation underway at Fentress Co. Sheriff's Dept.

Fentress County Attorney Leslie Clark Ledbetter told WBIR 10News she received an email from Cravens and his attorney Friday evening submitting his resignation.

His resignation will be effective April 28. 

She said the county commission and the county executive have not had a chance to meet yet to determine their plans moving forward for the sheriff's department. 

Clark Ledbetter said county officials will meet to review their policies on Monday.

Fentress County Sheriff's Department Chief Deputy Gary Ledbetter told 10News he "feels confident" the investigation is the reason Cravens resigned.

Ledbetter said he will be in charge of the department until the next sheriff is appointed. He said the county commission will appoint the next sheriff. 

Ledbetter said the sheriff's department itself was never under investigation, only the sheriff. 

"We are here for the people, and we are going to focus on that," he said. 

The full text of Cravens' resignation letter is below: 

"Dear Commissioners,

Please accept this email, sent via my lawyer, as confirmation of my resignation as Sheriff of Fentress County, effective April 28, 2017. A letter will follow under separate cover.

It was an honor to serve the people of this county, and I deeply regret the circumstances that have led to my resignation.

Chucky Cravens"