BERLIN (REUTERS) - German police have arrested two men suspected of supporting Islamic State in Iraq and Syria (ISIS) and raided properties across the country of another 13 suspected supporters of militant Islamist groups, prosecutors said on Saturday.

The two men were arrested in the western city of Aachen and identified as a 38-year-old Tunisian, Kamel Ben Yahia S., and a 28-year-old Russian, Yusup G., said federal prosecutors in a statement.

The Tunisian is suspected of providing clothing worth over 1,100 euros and 3,400 euros in cash to Islamic State since July 2013 and of smuggling a 17-year old boy from Germany to Syria via Turkey to join the group. The Russian is accused of helping the smuggling and of being a member of a foreign terrorist organisation.

Authorities believe the other suspects supported either Islamic State or Ahrar al-Sham, another Syrian Islamist group, by providing thousands of boots and other military clothing.

The raids took place in the western states of North Rhine-Westphalia, Hesse, Baden-Wuerttemberg, Hamburg, Rhineland-Palatinate, Schleswig Holstein and also the eastern state of Saxony.

Germany, along with other western European countries, is struggling to stop the radicalisation of young Muslims, some of whom volunteer to become militants in Syria or Iraq. Officials worry that they will return to plot attacks on home soil.

German intelligence authorities estimate at least 450 people have left Germany for Syria and around 150 have returned. Many are being criminally investigated.