French police hunting a serial rapist have come to a dead end after DNA led them to identical twins.

Police in Marseille are unable to determine which brother is the rapist because their genes are the same. DNA evidence was found on the female victims.

One of the 24-year-old twins, who are known only as Elwin and Yohan, is thought to have raped six women aged between 22 and 76 over the four months to January.

All six of the attacks took place in the entrance halls of stairwells, and their phones were stolen by the attacker.

CCTV footage from a bus led police to the apartment that the brothers share. One of the victim's mobile phones was also found at the twins' apartment.

However, their identical genes mean investigators cannot tell them apart. The women who were raped were able to identify their attacker, but could not tell which of the two brothers it was.

Both of the twins, who are unemployed delivery drivers, deny rape and they have been held in custody since Friday.

A source close to the case told Le Parisien: "They are real identical twins, nothing really distinguishes them, and they repeatedly use and lean on the fact that they are twins."

Emmanuel Kiehl, the chief investigator, said this was an unusual investigation: "It's a rather rare case for the alleged perpetrators to be identical twins. We must determine the exact role of each one."

Experts say it could cost around £850,000 to conduct a sophisticated genetic test to determine which twin is the rapist. Without such an extensive test, police say it will be difficult to determine which of the twins were responsible for the attacks, or if both were involved.

However, according to French newspaper La Province, it is unlikely that the Department of Justice will pay for such a test and that further evidence would be needed to establish which of the twins attacked the women.

An expert explained that under normal circumstances around 400 sets of base DNA pairings are compared. With the twins, they said, billions would need to be examined.