Sinn Féin’s Gerry Adams was forced to call off a visit to the US after restrictions were placed on him by the US State Department on a visa to travel to New York.
Mr Adams was barred from attending a fundraising dinner for his party unless Sinn Féin endorse current policing structures in the North of Ireland.
The issue of policing reform remains the subject of delicate political negotiations in Belfast as efforts continue to restore a local power-sharing administration.
The US State Department’s intervention represents an overt and potentially dangerous alliance with Britain and unionists in the peace process.
Mr Adams said he will fulfil a visit to Toronto on Saturday which had been planned to end a brief North American tour.
“I have been told I do not have permission to fund raise in the United States.
“I have to say that this is a rather amateurish effort by elements within the US administration to get Sinn Féin to change our position on policing.
“Our position on policing is very clear. The British government has agreed to honour certain commitments. I am committed if and when they do that to go to the Sinn Féin ard chomhairle (national executive) to deal with the issue of policing.
“These positions are matters of public record.”
Although Sinn Féin is being pressured to take its seats on policing structures, policing reform promised under the 1998 Good Friday Agreement has not yet been fully implemented.
Nationalists remain generally hostile to the North’s traditionally anti-Catholic police, and few have considered joining the force alongside known human rights abusers.
In addition, the failure of the British government to transfer policing and justice powers from London to the Belfast Assembly identifies the force with direct British rule, something which is anathema to republicans.
Mr Adams was to attend the Friends of Sinn Féin annual fundraising dinner in New York this week and had also planned meetings with US politicians before heading to Canada.
He was also due to receive an award from the National Committee on American Foreign Policy headed by Irish-American businessman Bill Flynn.
The visa offered by the US administration would only have let Mr Adams to attend the prize-giving ceremony which was a fundraising event for that organisation, but would have been banned from attending the Friends of Sinn Féin event.
“The visa position, as I understand it, is absurd,” Mr Adams said.
“It appears they expect me to go to New York and not go to any fundraising event. I am a busy man and have no wish to be just sitting around in New York.
“What they are doing is robbing me of the opportunity to convey to thousands of supporters in the United States the progress that has been made recently and the progress that can be made in the months ahead.”