Mosques and flats have been stormed by 800 Austrian police in a bid to break the network of a preacher suspected of brainwashing teenagers to fight for ISIS.

Authorities say eight people have been arrested after the huge anti-terror raids which took place across Graz and in the capital Vienna.

Officers entered apartments and unofficial mosques in the two cities as part of the crackdown, which targeted people from the former Yugoslavia suspected of establishing a jihadist network in Austria, according to Austrian media.

The raids were reportedly not connected to last week’s arrest of a suspected 17-year-old Islamist extremist in Vienna.

Instead, police said the raids allegedly focused on the network of a Muslim preacher from Bosnia who was jailed for 20 years last July in Graz for recruiting young fighters to ISIS.

The accused, known as Ebu Tejma, is thought to have ‘brainwashed’ dozens of people aged between 14 and 30 and enlisted a number of them to fight for ISIS in Syria.

Tejma fled from Bosnia to Vienna following the break-up of Yugoslavia and preached in various Austrian and southern German cities, becoming a ‘key figure’ in pushing IS propaganda, according to the prosecution.

He was arrested during a far-reaching crackdown on Austrian jihadist networks in 2014 and has denied the charges against him.

Austria has so far been spared by the string of attacks by Islamist extremists in other European countries in recent years.

But around 300 people have either left or were intercepted trying to leave Austria to fight in Syria, according to the interior ministry. Around 40 have died there while some 90 have come back.

On Friday, police detained an Austrian national of Albanian origin for allegedly planning a terror attack in Vienna.