The issue of photographs of IRA decommissioning remains on the agenda of Tony Blair and Bertie Ahern, US Envoy Mitchell Reiss has said.
US special envoy Mitchell Reiss took part in the Leeds Castle talks
Mr Reiss devised the proposal on photographic proof of IRA disarmament adopted by the two prime ministers.
The DUP is arguing that photographs are necessary to ensure that there is confidence in any act of decommissioning by the IRA.
But Sinn Fein say the IRA will "not submit to a process of humiliation".
Proposals published jointly by the two governments earlier this month included a plan for the IRA to allow photographs to be taken of its weapons being put beyond use in the presence of independent witnesses.
Republicans have argued the issue of photographs was dead and buried, but Dr Reiss said compromise ideas being discussed by the governments and the parties still included photographs.
Speaking to the BBC's Inside Politics programme, he talked for the first time about his role behind the scenes at the intensive talks in September at Leeds Castle in Kent.
He said he suggested a compromise proposal which would have seen photographs being taken of IRA disarmament before the end of this year but their publication delayed until the establishment of a new Stormont executive in the spring.
"There was an opportunity to try and see if we could bridge the divide between the DUP and Sinn Fein over photos and so it seemed to me that it might be possible to delay the publication of the photos as a way to address the concerns on both sides," he said.
"So I put that idea to the governments, they liked it and it was incorporated into the final document."
Dr Reiss said it was "premature" to claim photographs were now completely off the agenda.
Without going into details, he confirmed that photography was still involved in the compromise ideas being considered by the governments to break the deadlock.
Dr Reiss also warned that foreign investment in Northern Ireland might not increase in the future if a lasting political settlement was not reached.
The US administration believes its role in Northern Ireland is to build bridges between the parties and, where possible, to suggest ways in which obstacles can be overcome.
The political institutions in Northern Ireland have been suspended since October 2002 amid allegations of IRA intelligence gathering at the Northern Ireland Office.
The DUP and Sinn Fein became the largest unionist and nationalist parties after assembly elections in November 2003.
However, the two parties have not been able to reach a deal which would allow a power-sharing executive to be formed, and Northern Ireland continues to be governed by direct rule from Westminster.