The British Conservative leader has said conditions laid down by the Taoiseach for Sinn Féin participation in government in Dublin should also apply in Belfast.
Making his first trip to Northern Ireland as leader of the opposition, Mr Michael Howard said the IRA must verifiably get rid of its weapons and disband before Sinn Féin could join any administration North or South.
He also pledged that if direct rule continued beyond next year's expected general election, no Conservative government would move towards joint authority with Dublin without the consent of the people.
Addressing a meeting in Belfast, Mr Howard said: "What we need is the clearest demonstration - through deeds, not just words - that the republican movement has completed the transition to 'exclusively democratic and peaceful means'. That must include transparent decommissioning to an agreed timetable, an end to the IRA as an active paramilitary group and a clear acknowledgment that the so-called war really is over."
Commenting on the recent statement by Mr Ahern concerning an end to all paramilitary activity, he said: "I agree. But the standard that Bertie Ahern insists upon in Dublin should be the same standard that applies here in Belfast . . . under a Conservative government there will be no question of any moves towards joint authority or joint sovereignty by stealth or otherwise."