An Ulster Unionist warning that the latest political deal in Northern Ireland is in danger of unravelling has been dismissed by Stormont's Deputy First Minister as "silly".
Sinn Fein's Martin McGuinness rejected claims from UUP leader Mike Nesbitt that some parties were trying to re-negotiate parts of the accord.
Mr McGuinness said the implementation of the agreement, which resolved a range of contentious disputes that had destabilised the powersharing executive, was well on track.
The Sinn Fein veteran and Mr Nesbitt joined the leaders of the other three Executive parties at Stormont House today for talks with Northern Ireland Secretary Theresa Villiers and Irish Foreign Affairs Minister Charlie Flanagan about how and when the proposals they all agreed in December will be actioned.
The deal includes measures that addressed a budgetary crisis at Stormont; will see the long delayed implementation of the UK Government's welfare reforms in the region; and the establishment of new mechanisms to deal with the toxic legacy of the past.
Mr Nesbitt reiterated his concerns that others were trying to renegotiate elements of the deal as he emerged from the meeting.
"There is concern that it will unravel if people use this process to renegotiate rather than bring on what was agreed," he said.
"So if we are going to implement we implement what was agreed in December - we don't try to get bits that we failed to get in last year and try to sneak them in this time around."
But Mr McGuinness accused Mr Nesbitt of "politicking".
"I think we all have to approach this in a positive spirit, a constructive spirit, showing real leadership and I think, in terms of how we move forward, unfortunate terms such as the prospect of 'unravelling' do not sit well with the progress we have made over the course of recent times," he said.
"I think that was a particular silly comment to make given the fact that all of the meetings so far have been very positive, they have been very inclusive."
He added: "I haven't seen any attempt by any of the parties thus far to renegotiate the agreement that has been made and I think to make that remark in advance of a meeting which was a very positive and constructive meeting probably has more to do with politicking than anything else and I am going to rise above all of that."
Ms Villiers described the implementation meeting as "remarkably positive and cheerful".
"I think the Stormont House Agreement is a significant step forward for Northern Ireland and, of course, the key challenge now is getting it up and running and implemented in practice - that is crucial," she added.
"The UK government is committed to seeing it implemented fully and fairly and faithfully and I have been very pleased by the response from Northern Ireland's political leaders this morning.
"They are clearly working hard to fulfil their side of the agreement."
Ms Villiers said it was crucial the deal was not derailed, highlighting that if an agreement had not been reached the Assembly would be facing potential collapse.
"So it is crucial that the agreement isn't derailed, but I got a very clear and strong assurance from all the party leaders that they were working positively and constructively to see the agreement implemented," she said.
Mr Flanagan said: "I am confident that the NI Executive parties, together with the two governments, will continue to demonstrate the focus and leadership that led to the Stormont House Agreement, as we now make the commitments of that agreement a reality."