The army general overseeing the reconstruction of Notre Dame cathedral in Paris has said the building's chief architect should "shut his mouth".
General Jean-Louis Georgelin and architect Philippe Villeneuve disagree over whether the cathedral's new spire should look modern or medieval.
Notre Dame caught fire in April, losing its spire, roof and many artefacts.
French President Emmanuel Macron has set a five-year deadline for completing the huge restoration project.
Some experts warn that this target may be too ambitious - and Mr Villeneuve has previously said the only way it can be met is if the spire is a replica of the one that burned down.
But President Macron and General Georgelin both believe the new spire should be "contemporary".
A public argument over the spire's design broke out at a meeting of the French National Assembly's cultural affairs committee late on Wednesday.
"As for the chief architect, I have already explained that he should shut his mouth," General Georgelin snapped, prompting gasps from those at the meeting, AFP news agency reported.
He later said that all involved ought to "move ahead in wisdom so that we can serenely make the best choice for Notre Dame, for Paris, for the world".
A final decision on the spire would be settled on in 2021, he added.
On the same day, France 3 TV channel broadcast footage from inside Notre Dame - showing its missing spire and burned-out roof, as well as debris that has collected on the cathedral floor.
Last month, Mr Villeneuve told the broadcaster RTL: "Either I restore it identically... or they make a contemporary spire and it will be someone else [doing it]."
Within 24 hours of the fire on 15 April, hundreds of millions of euros were pledged to help fund the rebuilding of the cathedral.