Warren made the announcement Tuesday during a virtual city council meeting ... adding there may be a number of others that will decide to leave as well. The Mayor -- who did NOT ask for chief La'Ron Singletary's resignation following Daniel Prude's death -- said she doesn't know who will take over the embattled department on the interim basis ... considering since this all happened just moments ago.

What's more ... Warren said Singletary felt his career and integrity had been challenged after a graphic video of the March 23 arrest surfaced showing the 41-year-old Black man having a hood placed over his head by police. They are then seen pressing his face into the ground for 2 minutes until Prude stops breathing ... leading to his death days later.

Remember ... Warren admonished Singletary last week for failing to fully and accurately inform her about what transpired during the arrest. For his part, Singletary said "As a man of integrity, I will not sit idly by while outside entities attempt to destroy my character. The events over the past week are an attempt to destroy my character and integrity."

He added, "The members of the Rochester Police Department and the Greater Rochester Community know my reputation and know what I stand for."

Deputy Chief Joseph Morabito, a 34-year veteran at the department, also retired and said, "It has been my extreme honor to serve with and lead the most dedicated law enforcement professionals in the country. It has also been my honor to serve this community through these many years; a community I was born and raised in, and deeply love."

We reached out to the Rochester PD and are told the only officials retiring are Singletary and Morabito ... but as Warren said, more announcements could be coming soon.