U.S. President Donald Trump caused anger in France and Britain by suggesting looser gun laws could have helped prevent deadly attacks in Paris in 2015 and linking knife crime in London to a handgun ban.

In a speech to the National Rifle Association (NRA) on Friday, Trump mimicked the shooting of victims in the Paris rampage and said if civilians had been armed "it would have been a whole different story."

The French government issued its strongest criticism of Trump since he took office and one minister urged the leader to apologize, at a time when President Emmanuel Macron has been reinforcing bilateral ties following a state visit.

"France expresses its firm disapproval of President Trump's comments about the Paris attacks on Nov. 13, 2015 and demands that the memory of the victims be respected," the foreign office said in a statement.

"France is proud to be a country where acquiring and carrying firearms is strictly regulated."

French Finance Minister Bruno Le Maire said he hoped Trump "would come back on his words and express regret".

"His comments are shocking and not worthy of the president of the world's greatest superpower," Le Maire told BFM television on Sunday.

Other French politicians, including the mayor of Paris, took issue with Trump's comments, after he acted out the scene of the massacre by Islamist assailants at Paris' Bataclan concert hall, where 90 of the 130 victims of the attacks died.

"They took their time and gunned them down one by one. Boom! Come over here. Boom! Come over here. Boom!," Trump said, using his hands in a gun gesture.

Francois Hollande, who was French president at the time, said on Twitter Trump's remarks were "shameful" and "obscene".