The IRA is set to issue a statement on its future, Sinn Fein President Gerry Adams has confirmed.
There are expectations that an IRA statement is imminent
Expectations of a statement on Thursday rose following the release of Shankill bomber Sean Kelly.
Unionist attention will focus on whether the expected IRA statement will indicate that it will give up all its arms and give up violence for good.
Mr Adams said: "The forthcoming IRA statement will challenge Irish republicans and nationalists."
He appealed to "everyone to carefully read what the Army has to say and to remain united and steadfast".
"The IRA statement will also challenge others, especially the two governments and the Unionists," he said.
The group has been expected to give its response to a call by the Sinn Fein president to pursue its goals through purely political means.
Sean Kelly was one of two IRA men who bombed a shop on the loyalist Shankill Road in 1993 killing nine people.
The government said he was "released on the expectation of a forthcoming IRA statement".
Kelly's early release licence was suspended by Northern Ireland Secretary Peter Hain last month after security information indicated he had become "re-involved in terrorism".
DUP leader Ian Paisley branded the release of Kelly as a "government sop to the IRA".
Speaking after meeting Mr Hain on Thursday, Mr Paisley said the real proof of the IRA's future intentions would come in the months ahead.
"We've heard it all before... but we want the action that proves this has happened," he said.
Ulster Unionist leader Sir Reg Empey said the release of Kelly meant the government was "grovelling to republicans".
He added that the move "would be seen as a cynical manipulation, not only of the legal process, but the political process".
Meanwhile, Sinn Fein's Martin McGuinness has travelled to the US and is due to brief Mitchell Reiss, President Bush's special adviser on Northern Ireland, on Thursday.
He is also due to hold a news conference in Washington with a number of congressmen.
Martin McGuiness has travelled to America
BBC Northern Ireland political correspondent Martina Purdy said political reaction to the IRA statement would be critical and is expected to be mixed.
"Republicans will be looking for a warm welcome from the prime minister and the taoiseach," she said.
"Critically, republicans will want Tony Blair to keep his promise that if there are acts of completion by the IRA, he will implement the agreement in full, which means dealing with demilitarisation, for example.
"DUP leader Ian Paisley has already signalled that he is interested in 'deeds not words' from the IRA - and has said he wants a lengthy testing period."