Prime Minister Boris Johnson has been urged to apologise for an article he wrote in 1997 about the Srebrenica massacre, in which he described "these Muslims" as not "exactly angels".
In a letter with 30 other MPs, Labour's Tony Lloyd said there can be "no excuse for in any way blaming the victims of a genocide for its perpetration".
But Downing Street said the comments had been taken out of context
It is 25 years since 8,000 Muslims were killed at Srebrenica.
The massacre took place during the Bosnian War (1992-1995) when the Serb army was engaged in an ethnic-cleansing operation.
Thousands of Muslims sought safety in Srebrenica, which the UN was protecting with Dutch forces, but the area fell in July 1995 during a Serb offensive led by General Ratko Mladic.
Writing two years later in the Ottawa Citizen, Mr Johnson condemned what had happened, describing it as "the worst massacre on European soil since the Third Reich", but argued that it would have been difficult for the West to intervene in the conflict.
"Alright, I say, the fate of Srebrenica was appalling. But they weren't exactly angels, these Muslims," he said.
In the letter, more than 100 Muslim organisations and community representatives urged Mr Johnson to apologise, arguing that attending events commemorating Srebrenica "without reflection on your previous comments is an insult to the victims and their families".
Responding to the letter Downing Street said: "This quote is clearly taken out of context.
"The prime minister has, over the last 25 years, consistently condemned the Srebrenica genocide as one of the worst crimes in history."