The row between Sinn Fein and one of president George Bush's top advisers intensified today, as the party hit back at claims that it told "massive untruths" about policing in Northern Ireland.
Chief negotiator Mr Martin McGuinness defended claims, made two weeks ago, that the Police Service of Northern Ireland was deeply flawed.
The accusations, made in a £13,000 advert in the New York Times, prompted a stinging response by Mr Mitchell Reiss, Northern Ireland adviser to president Bush.
He said of the advertisement: "At best it was enormously misleading, at worst it was untruthful."
He urged Sinn Fein to reconsider its position and end its boycott of the policing board in Northern Ireland.
But in another round of adverts today - in the Irish Voiceand Irish Echonewspapers in New York - Mr McGuinness wrote that he was "happy to defend the ad point by point".
He claimed that Britain remained firmly in control of policing in Northern Ireland.
"Instead of the required civic policing, the intelligence agencies such as MI5, Special Branch and civil servants who have handled policing and justice for generations are still in charge," he wrote.
He went on: "Policing remains directly under the political control of the British government and its agencies.
"There is no timetable for the ending of British government control," he added.
The Mid-Ulster MP defended claims in the original Sinn Fein advert that "key positions are held by human rights abusers" and "collusion with loyalist death squads continues".
He wrote: "Special Branch still controls dozens of agents in the Loyalist paramilitary groups who act with impunity from the legal process."
He also repeated the accusation that Chief Constable Hugh Orde was opposed to inquiries which may expose human rights abuses.
Mr McGuinness claimed Mr Orde was against inquiries into the killings of Catholic solicitors Pat Finucane and Rosemary Nelson.