Sinn Fein has indicated that the proposals it introduced in July to break the impasse in the peace process are still on the table.
At a news conference, at which the party's submission to Senator George Mitchell at the start of the review was released, the Sinn Fein vice-president, Mr Pat Doherty, said his party was approaching the review "constructively" but that the approach of the Ulster Unionists did not give rise to optimism.
He said there was a collective responsibility on all the parties to achieve arms decommissioning and Sinn Fein would shoulder "no singular or special responsibility" on the issue.
Sinn Fein, in the "Defending the Good Friday Agreement" document, said that without the implementation of the agreement, arms decommissioning would be "virtually impossible" to achieve.
Mr Doherty said if the UUP leader, Mr David Trimble, took the lead within unionism and implemented the Belfast Agreement in full, then "of course" his party would "attempt to help". However, he added it was "very, very difficult to attempt to help someone who doesn't want to help themselves". The way to deal with every issue, "sequencing if you like", was contained in the Belfast Agreement. "It is contained in the Good Friday agreement how the executive has to be established. We made the historic compromise on Good Friday and that's the way forward," he said. But the inclusion of anti-agreement MP Mr Jeffrey Donaldson in the UUP negotiating team "did not augur well".
Ms Bairbre de Brun said the Belfast Agreement remained the party's "Plan A, our Plan B, and our Plan C - that is what we are working on within the review".
On the proposal to break the impasse tabled by Sinn Fein during the negotiations at Castle Buildings in July, which the British Prime Minister, Mr Tony Blair, described as a "seismic shift" in the republican position on decommissioning, Ms de Brun said the document had been rejected and was not under discussion.
"The problem for us is that the UUP rejected that document. They refused even to let us talk to their wider political party. They rejected it, they took it off the table and that is where it stands at the moment," she said.
Ulster Unionists had refused everything, had taken 15 minutes to say "No" to two governments and had consistently said "No" to the Belfast Agreement. "I can't tell at this stage, what it is, if anything, they would say `Yes' to," said Ms de Brun.
However, the Dublin Sinn Fein councillor, Mr Sean Crowe, added that the document had not been withdrawn. "The proposal is there if parties want it back on the table."
Commenting on Tuesday's meeting between the Sinn Fein president, Mr Gerry Adams, and Mr Trimble, which was chaired by Senator Mitchell, Mr Crowe said that every meeting with the UUP was seen by his party as a "positive step forward". Mr Trimble did not speak to reporters as he left the two-hour meeting and Ms de Brun said this enabled people to "judge his mood as well as we could".
The party said the British government should stand up to the unionist veto and implement the aspects of the agreement outside this veto.
Mr Conor Murphy, the Sinn Fein Assembly member for Newry and Armagh, said the British government had yet to produce the long-overdue demilitarisation schedule and claimed a "huge military operation" was still ongoing in south Armagh.