"The causes of the cut, which is located in the Mediterranean between Sicily and Tunisia, on sections linking Sicily to Egypt, remain unclear," the company said in a statement.
It was thought unlikely that an attack was the cause of the disruption, rather the cables may have been caught in trawlers' nets or an underwater landslide may have occurred, a spokesperson later said.
A ship was being sent to repair the lines, the firm said, but it may not arrive until Monday and it could take until December 31 for facilities to be fully restored.
Some services in Egypt were reinstated by diverting communications traffic through the Red Sea, a local official said.
The majority of business to business traffic between Europe and Asia was re-directed through the United States.
One cable is thought to be fully severed and the other two partially cut.
"If there was just one cable down we could have used the other two," Louis-Michel Aymard, a France Telecom spokesman, said.
"But all three are down so this puts us in a very difficult situation.
"This is a very rare situation," he said.