Diplomats from Indonesia, Egypt, Pakistan, Morocco and Tunisia said in a joint letter to the daily Aftenposten on Monday that opposition Progress Party leader Carl Hagen had insulted 1.3 billion Muslims worldwide.
Hagen, addressing a Christian congregation in Bergen, western Norway, earlier this month, used words widely taken to refer to the use of "suicide" bombers.
"We Christians are very concerned about the children. 'Let the children come to me,' Jesus said.
"I cannot understand that Muhammad said the same. In that case, it had to have been: 'Let the children come to me so that I can abuse them in my fight for Islamisation of the world.'"
Hagen added that Israel should be defended to help prevent the spread of "terrorism".
But in the letter published in Aftenposten, the diplomats said Hagen had "violated the principles of tolerance, understanding and cultural freedom that form the bedrock of Norwegian society".
They wrote that they found it difficult to find any justification for his harsh language, and labelled his remarks as "inappropriate for a politician in his position."
"My message is that Muslim fundamentalists are behind most of the terrorism in the world"
Islamic scholars have often rejected accusations that Islam promotes terrorism, although many argue that human bombings in Israel are justified as a last resort against overwhelming miltary odds.
Following the letter's publication, populist Hagen, who has in the past rejected comparisons to European far-right hardliners, was unrepentant, saying he had been speaking about Muslim "fundamentalists" and "terrorists" - not about Muslims in general.
"My message is that Muslim fundamentalists are behind most of the terrorism in the world," Hagen said on Monday, adding he was "surprised and partly shocked" by the reaction from the envoys.
"(The diplomats) are making themselves speakers on behalf of a religion... that is not their job," Hagen said. "Ambassadors represent states, not a religion."
Hagen's speech has sparked wide public debate in Norway over freedom of speech versus cultural and religious tolerance in a country that is still largely homogeneous after only a few decades of immigration.
"[Hagen has] violated the principles of tolerance, understanding and cultural freedom that form the bedrock of Norwegian society"
Letter from Muslim diplomats in Norway
"The debate has moved to morals," said Aftenposten in an editorial on Monday. "That is a highly legitimate issue, which needs to be discussed also in Norway."
Diplomats in Lutheran Norway seldom get involved in domestic affairs, and even more rarely do they jointly speak their views.
The anti-immigration Progress Party is the third biggest party in Norway's parliament and often tops political opinion polls.