The Fiji police say the assistant commissioner Henry Brown has resigned after being told to go on leave last month for unspecified reasons.
In a statement, the acting commissioner Brigadier General Sitiveni Qiliho says he received an email from Mr Brown yesterday stating his decision to leave the force.
Brigadier General Qiliho says Mr Brown indicated he is tendering the resignation under duress because of allegations against him.
Mr Brown was accused of unspecified wrongoing and an internal investigation was initiated against him.
Invoking the supremacy of the constitution, Brigadier General Qiliho sent Mr Brown on leave last month.
Brigadier General Qiliho says Mr Brown was on leave with full pay to ensure investigations were conducted thoroughly and fairly.
He says the first phase of the investigation is complete, and the file has been sent to the Director of Public Prosecutions for legal opinion.
He says Mr Brown's claim he has been denied natural justice is incorrect.
The Police Act makes no provison for sending an officer on leave but gives the commissioner the power to suspend an officer.
Last month, Brigadier General Qiliho said he would apply for the commissioner's job, saying he believed he has the right set of skills for the job.
He was put in charge of the police force in November when Ben Groenewald resigned as commissioner, citing interference by the military in police operations.
Mr Brown could not be reached for comment.