Conor McGregor has told bitter rival Nate Diaz that he should have "killed" him during their two-fight rivalry in 2016.
The pair have had an ongoing feud during their careers ever since their double-meeting five years ago.
Diaz won the first bout in the early part of the year with a second-round submission before losing the following meeting to McGregor via decision.
But McGregor has now escalated his rivalry further with Diaz by questioning his finishing abilities.
The Irishman posted on Twitter : "Me and all you pull out merchants are not the same! You are b**** made and I’m now steel.
"This game has just begun. Know that all my enemies are of similar age and experience, and for this reason, I hereby declare this war forever!"
And Diaz quickly replied : "War was declared along time ago you were already killed."
McGregor then clapped back in a final, now-deleted tweet: "You should have killed me when you had a chance, but you are no killer."
The Irish star is pondering his return to the octagon having suffered a second consecutive defeat by Dustin Poirier.
He has teased the possibility of a trilogy with Diaz which came on the fifth anniversary of their explosive rematch.
But it seems he will more likely make a return to the 155lbs division in a bid for redemption after sliding down to ninth position in the rankings.
And he has been called out by the likes of Rafael Dos Anjos, Michael Chandler and Max Holloway as he eyes a return to winning ways.
Diaz has just one fight remaining on his current deal with the UFC and is reportedly eyeing the creation of his own promotional label.
Should Conor McGregor and Nate Diaz face-off in a trilogy? Let us know your verdict in the comments section below
Meanwhile, McGregor has two fights remaining on his deal and will be eyeing a return to the summit by demanding he is handed a world title shot.
But UFC legend Chael Sonnen has called for the pair to make their own fighting group outside of the promotion to gain better reward for their reputation.
"Stop trying to be the world champion, stop," Sonnen told his YouTube channel. Stop. You, Conor McGregor and anybody with the last name of Diaz, you get to play by different rules.
"You're the only ones. You three knuckle heads go find each other and don't look for anybody else. Nobody gets to come up into your elitist group because nobody's done as good a job as you guys have.
"It's you three and you three need to figure this out. Masvidal needs to be in there either with Nate Diaz, with Nick Diaz, or with Conor McGregor. Conor McGregor needs to be there with either Nick Diaz, Nate Diaz, or Jorge Masvidal.
"It makes all the sense in the world. Jorge and Conor and anybody named Diaz, they are above the champions, they're above the fray, they're above the pay-per-view points, they're above the sold out arenas."
