The Republic's Fine Gael leader Enda Kenny sparked a furious response from Gerry Adams for outlining why his party will not serve in government with Sinn Fein.
Mr Kenny was outlining for the first time during a visit to Stormont on Monday why he could not go into government with the republicans.
He said the economic policies of both parties were incompatible -- but claimed the main issue was the fact that the IRA army council had not yet been stood down.
It comes months after Mr Kenny was unable to outline exactly why he would not go into government with Sinn Fein during an appearance on 'The Late Late Show'.
The January appearance was one of a number of poor media performances which led Mr Kenny to promise to up his game. But Sinn Fein leader Mr Adams described Mr Kenny's comments as "offensive" and "silly".
Mr Kenny said the two parties were completely at odds over "economic and taxation and European policy".
"Secondly, and more importantly, in our 26 counties, in our republic, we have a situation where we have one army and one army only," he added.
"I cannot deal with Sinn Fein because the army council has never been stood down. This is an issue that, as far as I'm concerned, is fundamental to the constitution of our country.
"I have given Sinn Fein due credit for the distance that they've travelled. That journey, in terms of democratic politics, has not yet been completed.
"I do think it is important from a Sinn Fein perspective that they should understand my deep concern here that in the Irish republic we have only one army, therefore there is no need for any party to have an army council in a time of peace."
Mr Adams said Sinn Fein had "no intention" of going into government with Fine Gael -- moments before Sinn Fein Cavan-Monaghan TD Caoimhin O Caolain refused to rule it out.
Mr Adams said it was "deeply offensive that a senior politician from Leinster House doesn't uphold the democratic rights of that section of the electorate who vote republican".
"The IRA have long since left the stage. Quite frankly, most democrats and republicans and nationalists don't trust Fine Gael on the national question. They just don't get it.
"We welcome the fact that Fine Gael are here (at Stormont). They're not here often enough otherwise they wouldn't make such silly statements."