Unionists have criticised Tony Blair over a reference he made to "Protestant extremists" during a speech on global terrorism and religious intolerance.
He said Muslims who committed acts of terrorism were no more true to their faith than the "Protestant bigot" who murdered Catholics in Northern Ireland.
The DUP's Ian Paisley Junior said this was "ill-thought out and provocative".
Ulster Unionist leader Sir Reg Empey said the prime minister's remarks were "far-fetched" and "dangerous".
NI Secretary Peter Hain defended Mr Blair and said the PM had done more than any of his predecessors to end violence and murder in the province, from which "Protestants had suffered most".
"What he said has been taken completely out of context," he said.
Mr Blair's speech in London on Tuesday was the first of three on foreign policy and terrorism.
It comes three years after bombs started dropping on Baghdad at the start of the US-led campaign that resulted in the fall and eventual capture of former Iraqi President Saddam Hussein.
He told the audience at a Reuters event that religious extremism - including the term Islamist extremism - should be labelled as such.
Mr Blair said he realised his remarks were going to be controversial, but there was an "interesting debate" being conducted within government about how to counter extremism in British communities.
"There are those, perfectly decent-minded people, who say the extremists who commit these acts of terrorism are not true Muslims, and of course, they are right," he said.
"They are no more proper Muslims than the Protestant bigot who murders a Catholic in Northern Ireland is a proper Christian.
"But unfortunately, he's still a Protestant bigot.
Ian Paisley Junior said it was a studied insult by Mr Blair
"To say his religion is irrelevant is both completely to misunderstand his motive and to refuse to face up to the strain of extremism within his religion that has given rise to it."
Mr Blair said terrorism "will not be defeated until its ideas, the poison that warps the minds, its adherence, are confronted at their essence, at their core".
Unionist politicians in Northern Ireland reacted angrily to Mr Blair's comments, with the DUP's Ian Paisley Junior saying it was a "studied insult of the Protestant community".
"The prime minister's comments, singling out Protestantism as a root cause of terrorism, is so unbalanced that it not only reveals (his) true nature, but also identifies a weakness in his judgements, his character and his understanding," he said.
Meanwhile, former Presbyterian moderator Ken Newell said bigotry could be found in all religions and needed to be challenged, but Mr Blair's comments were not balanced.
"I think his words were unwise and unbalanced and he does point the finger at the Protestant community in particular," he said.
"I know for a fact that everyone within their own faith traditions realises that in those communities there are people who are extreme and very bigoted."