VIENNA (REUTERS) - Austria has detained two teenage girls after they tried to travel to Syria to marry fighters of the jihadist group Islamic State in Iraq and Syria (ISIS), a spokesman for the prosecution said on Sunday.

The girls, aged 16 and 17, had been sent back to Austria from Romania, where they were picked up by authorities on a train on Dec 30 as they tried to make their way to Syria to marry ISIS fighters there.

Around 170 people, many from Eastern Europe, have travelled to the Middle East from Austria to join Islamist militant groups, according to the Interior Ministry.

Austrian authorities in October detained on terrorism-related charges a 14-year-old boy who was allegedly planning to travel to Syria and had researched on the Internet how to build bombs.

The parents of the girls had handed over the phone of the 16-year old to Austrian authorities when she went missing in December. Data taken from a Russian chat application on the phone showed conversations about the girls' plans, a spokesman for the prosecutors in Salzburg said.

The girls were detained in their homes in Salzburg and the province of Upper Austria after they returned from Romania. The girls had Bosnian and Chechen family backgrounds, according to APA news agency.