CARIBOU, Maine — The head of the city’s fire, ambulance and emergency management services has resigned after more than four decades as a Caribou firefighter.

However, City Manager Steven Buck issued a statement Tuesday indicating that he accepted the resignation “in lieu of termination” after an investigation into a complaint filed against the fire chief by a city employee.

Roy Woods resigned late Monday after 44 years with the Caribou Fire and Ambulance Department, including 21 years as the head of fire, ambulance and emergency management services for the city. According to a copy of the resignation letter delivered to the city manager, Woods said he was resigning for “medical reasons.’’

In his letter, he says that “the stress of chief of fire, ambulance and EMS director for the city of Caribou for 21 years has become more than my wife and I can handle. For medical reasons, I must resign.”

Woods goes on to say that he “spent his life” working to protect the city, working his way up from firefighter to firefighter/paramedic instructor and eventually chief. He lauded his former workplace as “the best fire and ambulance department in the state.”

He also wishes the department “the best of luck” in the future.

In his statement to the media on Tuesday, Buck referred to an investigation into a complaint against Woods.

“An independent investigation into the personnel matter was conducted with an expanded scope,” said Buck. “After extensive review and evaluation of the results of the investigation, my own evaluation and after reviewing these evaluations with Woods and a subsequent review of his responses, I accepted his immediate resignation.”

Buck said that Maine law prevented him from commenting on a personnel matter, and the city would not release any additional details about the incident.

A new chief has not yet been appointed, but the current chain of command at the department is filling in until a new leader is appointed. Caribou Police Chief Mike Gahagan also is helping to oversee the department, and Buck said there would be no break in services.

He also said in the statement Tuesday that the city recognized Woods’ contributions and dedication over the past four decades.

“It is with extreme regret that he will no longer be of service to the city of Caribou,” he noted.

Woods could not be reached for comment Tuesday.

Woods was elected vice president of the Maine Fire Chiefs Association in 1999 and served as a director of the Aroostook County Fire Chiefs Association.