5:40 PM PT -- Diddy's legal team tells TMZ ... "Our written and oral communications with CNN’s counsel were clear - they destroyed the original video file they received from their source."

CNN is vehemently denying claims by Diddy's legal team that the cable news network altered footage of him beating Cassie in a hotel hallway and then destroyed the only known copy of the video.

A spokesperson for CNN tells TMZ ... "CNN never altered the video and did not destroy the original copy of the footage, which was retained by the source. CNN aired the story about the video several months before Combs was arrested."

We broke the story ... Diddy's defense team claimed Thursday in new court docs that CNN purchased the video showing Diddy attacking Cassie in the hallway of the InterContinental Hotel in L.A.

Diddy's camp claims CNN took the only known copy of the hotel's surveillance footage and uploaded it into a free editing software, altered the video and then destroyed the original footage.

But, CNN says Diddy's lawyers have it all wrong.

The Cassie beating video came out in May 2024, a few months before the feds arrested Diddy ... and after the footage was released on CNN, Diddy posted an apology video.