President Emmanuel Macron said on Wednesday he feared for trust in France's institutions after a botched investigation into the main suspect in an 11-year-old girl's likely murder triggered public outrage.

The body of the girl, named as Lyhanna, was found last week after she went missing on 29 May in the southwestern town of Fleurance.

The suspect, a 41-year-old father of a school friend of the victim, had twice before been formally accused of raping a child, but investigations had been dropped or had stalled.

"It is trust in our institutions that is at stake," Macron told a cabinet meeting, according to government spokesperson Maud Bregeon.

But he called for calm after nationwide anger over the handling of previous allegations against the main suspect, adding: "We do not respond to a tragedy with shouting."