Former DUP leader Arlene Foster and Alliance leader Naomi Long have been embroiled a bitter online spat over their policies on Stormont power-sharing.
The former First Minister accused Mrs Long of being "nasty", while the Justice Minister questioned Mrs Foster's leadership.
There were sharp exchanges on Twitter between the pair after Mrs Long called for reforms to enable a voluntary coalition government if the DUP refuses to rejoin the Executive following May's election.
Mrs Foster claimed Alliance had "not once" sought to change the rules during a three-year collapse of devolution after Sinn Féin walked out over the RHI controversy.
Read more: Arlene Foster signals she will stay in DUP after NI Assembly departure as new MLA confirmed
But Mrs Long rejected the claim, saying her party has "consistently called for reform of the institutions".
She said Alliance had raised proposals for reform throughout talks to restore Stormont but both the DUP and Sinn Féin "had red lines holding us all back".
In an apparent reference to Mrs Foster's past comments on the Renewable Heat Incentive controversy, Mrs Long added: "Maybe you just weren't over every jot and tittle?"
Mrs Foster hit back, tweeting: "And maybe you let us see how nasty you really are from time to time. #maskslips. #playtheball #nastyparty #alliance."
The spat continued, with Mrs Long asking the former DUP leader why she was sharing their exchanges via "quote-tweet" rather than simply replying within an existing thread.
She added: "As a campaigner against online bullying, you will know this is a classic way of instigating a pile-on. Do better, Arlene."
Mrs Foster responded: "Seriously - now I'm instigating a pile on. Do better yourself Naomi - try practising what you preach."
Mrs Foster stood down as DUP leader and Stormont First Minister last year following an internal revolt against her leadership.
Last July the former First Minister joined the news channel GB News as a regular contributor.
Read more: Arlene Foster signals she will stay in DUP after NI Assembly departure as new MLA confirmed
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