Some 100 German citizens have been killed while fighting alongside the Islamic State group in Iraq and Syria since 2012, German Interior Minister Thomas de Maiziere said Sunday. His comments were reportedly published by Germany's Bild am Sonntag newspaper.

De Maiziere said that about 700 people from Germany have traveled to Iraq and Syria in the last three years to fight alongside ISIS. Nearly a third of the citizens who left the country to join the militant group have since returned, he reportedly added.

According to the minister, the country issued a travel ban on Iraq and Syria amid growing concerns of radicalization. Recent changes in German law reportedly have given authorities right to confiscate identity documents of anyone seeking to travel to the Middle East to participate in "terrorism activities.”

ISIS, which has taken control over large parts of Iraq and Syria, has reportedly recruited thousands of Westerners to wage war against their own country. An estimated 30,000 foreigners are believed to be fighting alongside the Sunni militant group, media reports said, citing U.S. intelligence.

Earlier this month, Hans-Georg Maassen, the head of Germany's domestic intelligence, said that the number of Germans traveling to Syria and Iraq to fight for ISIS has reduced in the past few months in comparison to the surge seen last year following the group's declaration of a “caliphate.”

"We expect that the numbers will continue to increase, probably not as dramatically as we experienced last year, but ISIL, Syria and Iraq and this battlefield are still attractive for young people from Germany who want to become jihadists," Maassen told Reuters.

ISIS also released its first video in German this month, calling on Muslims in Austria and Germany to join the group’s fight against Western countries.