The US envoy on international religious freedom on Tuesday voiced concern about France, warning against "heavy-handed" measures as President Macron targets radical Islam. 

"I am concerned, obviously, for what's happening in France," Ambassador Sam Brownback told reporters when asked about Macron's initiative.

"I think there can be constructive engagements that I think can be helpful and not harmful. When you get heavy-handed, the situation can get worse."

Macron has ordered a crackdown on extremism amid shock in France over attacks carried out by radicalised Muslims.

Under the initiative, France -- which is avowedly secular and home to Europe's largest Muslim population -- will shut down mosques if they are found during inspections by authorities to be promoting extremism.

Macron's efforts have triggered protests in several Muslim-majority countries, with the leaders of Turkey and Pakistan alleging that he is attacking Islam.

Defenders of Macron have accused his critics pointing to severe repression of religious faith elsewhere in the world.