French President Francois Hollande warned Thursday that Europe would be entering "unknown" territory if Greeks voted against tough austerity conditions attached to a bailout in a make-or-break referendum.

"If the 'No' wins we're entering into the unknown. It's up to the Greeks," he told reporters on a trip to Benin, the first leg of a whistlestop African tour that will also take him to Angola and Cameroon.