Mr McGuinness said time was running out
Decision time on a political resolution in Northern Ireland is fast approaching, Sinn Fein's chief negotiator has said.
Speaking at Stormont on Monday, Martin McGuinness suggested that 31 October should be the deadline for breaking the political deadlock.
The Northern Ireland assembly will have been suspended for two years this week.
Mr McGuinness sent a clear signal to the Democratic Unionists that the fundamentals of the Good Friday Agreement, including the joint aspects of the first and deputy first minister's office were not open to negotiation.
Mr McGuinness said the DUP were trying to restore unionist rule at Stormont and said that would not happen in a million years.
"Are the DUP prepared to accept a comprehensive deal which is based on the core principles of the Good Friday Agreement or are they going to continue to attempt through the two governments to erode the power-sharing fundamentals of the Agreement as they attempt to reintroduce unionist rule?" he said.
"I have often said that I believe that the DUP and Sinn Fein will do a deal. So why not do this deal now?"
The DUP is seeking changes to the way the first and deputy first ministers are elected.
But Sinn Fein and the SDLP are insisting the DUP will not be able to change rules and escape voting for a republican deputy first minister.
Another point of contention is how soon the assembly can gain control of justice and policing.
Northern Ireland Secretary Paul Murphy, who returned to work on Monday after taking ill at the Labour Party conference, is due to meet the Irish Foreign Minister, Dermot Ahern, on Tuesday.
The political parties and the British and Irish Governments held negotiations at Leeds Castle, Kent, in September in an effort to conclude a deal which would see the restoration of the assembly.
However, the two governments were unable to get the Northern Ireland Assembly parties to sign up to a deal over power-sharing after unionists and nationalists clashed over future devolved institutions. The talks broke up without agreement.
The political institutions in Northern Ireland were suspended in October 2002 amid allegations of IRA intelligence gathering at the Northern Ireland Office.