The video, sent to KOMO the day after the October 18 incident, appears to show the officer in a physical confrontation with someone who was filming the police activity in the area with a cell phone camera.
When the person tries to get the attention of a nearby uniformed officer after apparently being hit, the undercover officer can be heard saying "I am an officer you (expletive)!"
Asked to comment on the new video, Seattle police officials declined to view it, citing the existing investigation into the officer.
The video was shot on a sidewalk outside a Seattle convenience store. It appears to show the same undercover officer who was captured on surveillance video inside the store kicking a suspect.
On Thursday, Seattle Police Deputy Chief Clark Kimerer said the surveillance video uncovered Wednesday showing the kicking incident was in a police file for two weeks and the department's command staff was unaware of its existence.
Police officials placed the officer on administrative leave Wednesday evening after viewing the video.
The officer works undercover and the suspect who was kicked had allegedly been involved in an earlier assault on that detective during an undercover buy.
"This might be a case where the use of force was potentially excessive," Kimerer said. "Our officers cannot afford to give into emotion and I think we give a very clear statement about that every time we can."
Kimerer said no one raised concerns about the officer's actions during the arrest until commanders were asked about the tape by media outlets.
"That is a concern and it is a focal point of the internal investigation," Kimerer said
Kimerer said he wants to know who watched the tape and why they never reported what they saw.
"Was there any dereliction in not informing the command staff of a possible violation of department policies and procedures?" Kimerer said of the questions being asked internally.
While police officials declined to comment on the confrontation filmed by cell phone after the arrest, a spokesperson issued a statement saying the department asked KOMO to provide a copy of the video, which can be viewed in full on this web page, to the Office of Professional Accountability, which is already investigating the officer.
The officer seen in the tape is one of several Seattle officers who have drawn criticism in recent months.
Diaz named Nick Metz as deputy chief of operations and community building. Eight other commanders have been given new responsibilities to help fight crime while developing closer ties with city residents.
On Aug. 30, Officer Ian Birk fatally shot 50-year-old John T. Williams. Members of Seattle's Native American community and civil rights advocates have criticized the officer's actions. An inquest into the death is upcoming.
Diaz has said his department will submit its investigation of the shooting to two other police agencies for an independent review.
Earlier, two Seattle officers were caught on video kicking and stomping on a man and using a racial epithet. They had taken him down as a robbery suspect but released him after they realized they had the wrong man.
Diaz ordered an internal investigation and apologized to the man, as did one of the officers.
A video emerged in June of an officer punching a 17-year-old girl after she shoved him as he tried to arrest her friend for jaywalking. The girl later apologized; Diaz ordered a review of police training procedures.
On Thursday afternoon, the American Civil Liberties Union of Washington called for a Justice Department investigation into the Seattle Police Department.
"Recently released footage of an incident during which a Seattle police officer is seen repeatedly kicking an African-American youth is yet another disturbing example in a string of recent incidents in which the Seattle Police Department has engaged in unnecessarily violent confrontations with citizens," the organization wrote in a news release.
The officer involved in the latest incidents captured on video has not been charged with any crimes, and it was not clear how long it would take for the Office of Professional Accountability to complete its investigation.
In a statement posted on the department's blog Thursday evening, officials said Diaz asked the OPA to "expedite the gathering of preliminary evidence" into the October 18 incident.
The statement said the review would determine whether an outside law enforcement agency should be brought in to take over the investigation.