oooh dear! Whoever is leaking Nicki Minaj's nudes should just STOP!!!

It's not fair! Someone posing as Safaree Samuels is tweeting out extremely NSFW pics of his ex, Nicki Minaj ... but the rapper is adamant ... he's got nothing to do with it.

A rep for Safaree tells TMZ ... he'd never do anything like this, and he's doing everything he can to shut down the tweeter behind it. The photos -- some in highly sexual situations -- started going out on Wednesday ... from a Twitter handle extremely similar to Safaree's.