A group of Syrian boys as young as seven have been arrested on suspicion of sexually assaulting girls at an indoor swimming pool in Germany.

The incident is said to have happened on Monday in Mariendorf, a borough in the capital Berlin.

Seven boys aged between seven and 14 surrounded and harassed several girls, police say.

The suspects allegedly swam behind the girls, surrounded them and then grabbed them by their bottoms and breasts.

According to the father of one of the girls, the boys completely surrounded their victims so they were unable to escape.

Pictured is the Berlin swimming pool where the alleged sex attack is said to have taken place (file photo)

The man had brought his daughters aged nine, 11 and 14, together with a 14-year-old friend, to the pool to celebrate his eldest daughter's birthday.

According to his statement, the 11-year-old girl managed to get away from the boys and found a life guard. The lifeguard immediately alerted the police.

The boys were arrested and taken to the police station to be questioned, after which they were handed over to their parents. They all received a one-year swimming pool ban.

A police spokeswoman said the group is being investigated for 'an offence on a sexual basis.'

Six of the boys are Syrians, and the authorities have yet determined the nationality of the seventh boy. One of the boys is 14 years old, while the rest of them are aged between seven and eleven years old.