Irish American politicians tonight called on Sinn Féin to endorse policing in Northern Ireland after they turned down policing board seats in the province.
But the group, led by Senator Edward Kennedy, also said it was essential the Rev Ian Paisley's Democratic Unionists committed themselves to taking part in an inclusive government with Gerry Adams' party.
The Friends of Ireland, a lobbying group of Congressmen and Senators, said in a statement that Sinn Féin must continue to build on the "significant progress" already made.
"Progress on policing is essential in order to ensure peace and stability in Northern Ireland," they said.
"A decision by Sinn Féin to support and join the new policing structures would be a very important step forward."
On Monday, Northern Ireland Secretary Peter Hain announced the new-look 19-member policing board for Northern Ireland which will sit for the first time on April 1.
The board will have four Democratic Unionists, two Ulster Unionists and two Assembly members from the nationalist SDLP, but Sinn Fein has turned down the two seats it was offered.
The party also refused to take its seats on the previous board because it believes policing reforms in Northern Ireland do not go far enough.
The Americans also called for justice to be done in the case of Robert McCartney and for paramilitaries to end "criminality and intimidation".
The group, which also includes Senators Chris Dodd and Susan Collins and Congresswoman Nancy Pelosi, said September's decommissioning by the IRA should have been embraced by all in the Unionist community.
"We regret that the Democratic Unionist Party has refused to state that it is willing to share power with all parties, including Sinn Féin, and has continued to reject the Good Friday Agreement," the group said.
"It is essential that the DUP unequivocally agree to share power with all parties, and commit itself to working within all the institutions established by the Agreement."
The statement came as Taoiseach Bertie Ahern met Senator Kennedy and other leading Irish American politicians, and said he would be looking to them later in the year to help convince Northern Ireland parties that working under the terms of the Belfast agreement was possible.