Sinn Fein President Gerry Adams has strongly criticised US President George Bush's special envoy to NI.
Gerry Adams believes Sinn Fein should be allowed to fundraise
Speaking in Washington, Mr Adams said: "I don't have high regards for Mitchell Reiss's input into this process."
"If it is he who is advising the president, it's very very bad advice," he added.
However, Mr Reiss has dismissed the criticism from the Sinn Fein president. "I reject that accusation, that allegation," he said.
Mr Adams is angry that the US government has refused him permission to fundraise, and said it was wrong to treat Sinn Fein differently.
He was speaking as he arrived at a Friends of Sinn Fein gala breakfast on Thursday.
The party has been forced to refund donations that were to be made at the event at Washington's Capitol Hilton hotel.
Mr Reiss said: "We try very hard to be an honest broker. I think if you look at the record, it demonstrates quite clearly that we don't play favourites - that we call it as we see it.
"We try to keep our eye on the main objective here - which is moving the peace process forward and keeping the focus on the people of Northern Ireland."
Northern Ireland Secretary Peter Hain, who is also in Washington, said the "clock is ticking" for the suspended assembly.
"There are some hard choices going to be faced by all the politicians this year because there needs to be a moment of decision made," he said.
"We can't continue with this state of political paralysis and impasse that we've had for far too long, with an assembly that hasn't met for nearly four years and with the whole cost from the taxpayer pouring in to fund that institution and its members."
Irish Prime Minister Bertie Ahern said: "The issue now is are people prepared to work together in an assembly, and work together as the Good Friday Agreement set out.
"I think we're going to find that out in the months immediately ahead."
Meanwhile, SDLP leader Mark Durkan rejected earlier Sinn Fein claims that the US government has become biased in its handling of the peace process.
Speaking in Washington, Mr Durkan said Mr Adams was wrong to criticise the Bush administration as partisan.
Mark Durkan is in Washington for the Saint Patrick's Day celebrations
He said the US had been critical of unionist politicians for their stance on the violence that erupted last year over the Whiterock parade
Speaking in New York before travelling to Washington for Saint Patrick's Day this Friday, Mr Adams said he was bewildered and surprised that the US government would not allow Sinn Fein to fundraise when the IRA had put all of its weapons beyond use.
Mr Durkan said he felt Mr Reiss had "done a good job in calling things straight on the need for a lawful society".
Mr Adams' comments also took some US politicians by surprise.