The victim was found on Sunday in the southern province of Kampot, a day after she was last seen alive leaving her guest house by bicycle, provincial deputy police chief In Chiva told AFP.
"We conclude that it is a murder case because she was seriously hacked on the forehead," he said, adding that there were also injuries to the victim's arms.
The French embassy said the family had been informed.
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"An investigation is ongoing to determine the exact cause of the death but according to first observations, the criminal option seems most likely," Nicolas Baudouin, first secretary at the embassy, told AFP by email.