US Special Envoy to Northern Ireland Mitchell Reiss said the International Monitoring Committee (IMC) report published yesterday showed clear progress was being made on issues critical to the peace process.
Mr Reiss was commenting on the IMC conclusion that the IRA cessation of activities was holding firm but that the threat from loyalist paramilitaries had not been removed.
He expressed concern about the threat posed by the loyalists, although the report said they had contributed to peaceful marching season this year.
The IMC said dissident republicans posed "the most significant security threat in Northern Ireland".
Ahead of next month's all-party talks in Scotland aimed at breaking the current impasse, the IMC's 11th report said the maintenance of the IRA structure was proving an important element in keeping the organisation on the path of peace.
"We note in particular the report's conclusion that the IRA is firmly committed to following a political path, is not engaged in terrorist activity and has taken a stance against criminality," Mr Reiss said.
"We are concerned, however, about the report's findings that dissident republicans pose a significant security threat and that some loyalist paramilitaries continue to engage in violence.
The British government has set a November 11th deadline for the restoration of power-sharing in the North and threatened to impose a "Plan B" strategy in conjunction with Dublin.