Berlin authorities have arrested four people for allegedly supporting terror group Isis (Islamic State).

The four were arrested during an anti-terror raid conducted to prevent people from carrying out terrorist attacks in the country.

Authorities raided four apartments in the Schöneberg area and arrested the four men, Turkish nationals, suspected of gathering equipment to aid IS' insurgents in Syria and Iraq.

The arrest came as 24-year-old German Ismail Issa is to be tried after he admitted he had returned to Germany from Syria to buy supplies for insurgents of the Islamic fighters in Syria, who have now joined IS.

The items he was in charge to buy included sports watches, combat trousers and night-vision gear, according to Focus Magazine.

Issa was arrested with another man in November 2013.

Germany officially banned IS from any activities in the country in September.

"The terror organisation Islamic State is a threat to public safety in Germany as well," Defence minister Thomas de Mazière said. "We are resolutely confronting this threat today.

"Today's ban is directed solely against terrorists who abuse religion for their criminal goals," he added. "Germany is a well-fortified democracy, there's no place here for a terrorist organisation which opposes the constitutional order as well as the notion of international understanding."