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Two young Syrian brothers have been arrested in a refugee camp in southern Austria on suspicion of belonging to terrorist groups, prosecutors said Wednesday, according to the AFP news agency.

Police detained the two men, aged 16 and 18, in the Leibnitz district in Styria state last Thursday after a tip-off from German authorities, the prosecutor's office in the city of Graz said.

While the younger brother is accused of belonging to the Islamic State (ISIS) group, his older sibling is thought to have fought for the Ahrar al-Sham militia, the office added.

Ahrar al-Sham is part of the Islamic Front, a coalition of seven Islamist rebel groups fighting in Syria against President Bashar Al-Assad, but also against ISIS.

The pair allegedly fought each other during the Syrian civil war, which has so far claimed more 250,000 lives and forced millions to flee their homes since it broke out in March 2011, according to AFP.

They face charges of committing terrorist acts, including attempted murder and torture, Austrian prosecutors said, adding that a third brother had been arrested in Germany.

Facing the challenges of Austrians travelling to the Middle East to join jihadist groups, Austria's parliament in February passed a law banning foreign sources of financing to Muslim organizations and requiring imams to be able to speak German.

In June, an Austrian court convicted nine people of Chechen origin who were arrested on their way to join ISIS terrorists together with their Turkish driver.

The nine, aged 18 to 28, were found guilty of belonging to a "terrorist" organization and given jail terms of between 19 months and three years, except for one who got a suspended sentence.

The latest arrests are likely to add fuel to an already heated debate in Austria over how to handle Europe's worst migrant crisis since 1945.

The Alpine nation of 8.5 million expects to see a record 95,000 asylum claims by the end of this year, compared to 28,000 for the whole of 2014.

Many of those arriving are unaccompanied boys and young men, which has prompted far-right and conservative politicians to warn that the refugee flow posed a threat to national security.

AFP contributed to this report.