Naomi Long has challenged the Government to get Unionist leaders back to the table for the "Haass talks" on parades, flags and the Troubles legacy.
Unionists abandoned all-party discussions earlier this month after the Parades Commission barred an Orange Order parade from marching past Ardoyne on the Twelfth of July.
Speaking at Northern Ireland Questions in the House of Commons on Wednesday, the East Belfast Alliance MP asked what was being done by the Northern Ireland Office to bring back the DUP and UUP.
“I was told the NIO would do everything in its power to bring the parties together in order to ensure a peaceful and prosperous future for the people of Northern Ireland,” said Mrs Long.
“However, this issue goes deeper than that, and takes in our past as well as our future. In order to deal with the issue of the past in a comprehensive way, we require momentum and that involves the parties sitting down to discuss and reach decisions on a number of areas.
“That will not happen if certain parties decide to act irresponsibly by leaving talks designed to create a solution to the impasses we are facing. The victims who have suffered deserve nothing less than all parties being fully committed to the process.”
In a joint statement issued on July 3 by DUP leader Peter Robinson, the UUP's Mike Nesbitt, TUV leader Jim Allister, PUP's Billy Hutchinson and Ian McLaughlin of the Ulster Political Research Group, the parties said the Parades Commission placed "no value on a relationship with unionism and have treated our advice with contempt."
Prime Minister David Cameron has since urged Northern Ireland's politicians to return to the talks to prevent extremist elements "pushing their ideas".