Two Swiss police officers have arrived in Corsica to assist their French counterparts in the search for the twin 6-year-old girls who disappeared almost two weeks ago.

Hope of finding the girls alive is fading after a letter from their father turned up declaring he had killed them and was planning to kill himself.

Matthias Kaspar Schepp took the twins to Corsica but left the French island alone. His body was found several days later in Italy.

A spokesman for police in the girls' home canton (state) of Vaud says the Swiss officers arrived in Corsica Saturday to "cooperate with the investigation."

Jean-Christophe Sauterel says despite the grim contents of the letter police will continue the search for Alessia and Livia until there is certainty about their fate.