The British domestic security agency MI5 has had a "long and painful history" of underhand operations in Northern Ireland that should not be copied in the US, former FBI director Louis Freeh has warned.
On Tuesday, the FBI made the unusual step of releasing Mr Freeh's comments as a press release on its website.
This is the first time that Mr Freeh has so openly criticised MI5, which worked closely with the FBI in operations against the IRA while Mr Freeh was FBI director.
In an angrily-worded editorial in the Wall Street Journal, Mr Freeh strongly rejected an argument by conservative federal circuit court judge Richard Posner that the US needs its own MI5 to counter terrorism. Describing Judge Posner's idea as "dangerous and dumb", Mr Freeh accused him of having an overly romantic concept of MI5.
"Judge Posner's citation to England's MI5 is romantic enough but needs to be qualified by the long and painful history of its operations in Northern Ireland, which are still unfolding after decades of secrecy and nontransparency," he wrote.
Mr Freeh warned that such an organisation could not be adequately trusted or monitored by the US public and accused Judge Posner of offering a "long-winded thesis" that could not work.
"I suppose that this secret-police agency would appear before Congress in closed sessions and operate with a black budget," Mr Freeh wrote, adding that the American public would never tolerate a CIA-type police organisation operating against US citizens and foreigners "who live and work under our flag".
He was responding to an editorial by Judge Posner, also in the Wall Street Journal, in which he said that Mr Freeh had tried and failed to get the FBI to take terrorism seriously and that it was now time for a US version of MI5.
Mr Freeh has worked very closely with British spy agencies and police, and had serious confrontations with Bill Clinton because of his insistence in prosecuting US-based IRA members during sensitive moments in the Irish peace process.
President Clinton and a former Miami FBI chief have publicly acknowledged that Clinton and Freeh had shouting matches over the president's opposition to prosecuting four Miami-based IRA gunrunners in the early 1990s.