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Greek police have arrested a Syrian refugee, whose swimmer sister competed in the 2016 Olympics, for helping migrants enter the country illegally.

Sarah Mardini, 23, was one of three members of an aid group arrested in what police described as an operation to dismantle a "criminal network".

She and her sister Yusra came to Europe after fleeing the Syrian war in 2015.

That year, the pair helped save more than a dozen migrants by pulling their broken-down boat to shore in Greece.

Ms Mardini's lawyer told AFP news agency his client had been volunteering on the island of Lesbos with Emergency Response Centre International when she was arrested along with a Greek and an Irish national.

She is being held at a prison outside of Athens, he added, describing the case as "criminalising help given to refugees".

Ms Mardini denies the charges against her.

More than 8,000 people are currently being held at the Moria camp on the island, in very poor conditions.

The two sisters left their family home in Damascus in August 2015 and travelled more than 1,000 miles to Germany.

They settled in Berlin, where Sarah was awarded a scholarship to study economics and social sciences at Bard College.

Her younger sister Yusra went on to represent the first Team Refugee at the Rio Olympics in 2016 and has since become a goodwill ambassador for the UN's refugee agency.