German police raided eight sites Tuesday -- including a mosque -- that they said were being used by Islamic extremists, the Associated Press reported. Among those arrested were a 51-year-old Moroccan and a 19-year-old Macedonian man who was believed to have gone to Syria to fight against the Syrian government. Another individual was arrested recently for allegedly trying to recruit Syrians in a refugee center to join Islamic State militants, various news outlets reported.

The arrests come as Germany launched a number of investigations into allegations of militants with the Islamic State group, also known as ISIS or ISIL, exploiting the influx of refugees in order to infiltrate Germany. In one case, a man was filmed telling others in his shelter about his ties with ISIS. Some images that have surfaced on social media in recent weeks, which allegedly show ISIS fighters in Europe, have been outed as fakes.

The ongoing Syrian war has sent some 370,000 refugees fleeing to Europe this year, the United Nations’ refugee agency has estimated. Among the refugees have also been migrants from African and other Middle Eastern and Central Asian countries. Several eastern European nations have sought to prevent refugees from entering, while Germany has offered to take in hundreds of thousands of refugees each year.

 

The German government said there haven't been any credible threats posed to the nation's security. However, an ISIS commander reportedly told BuzzFeed in January that thousands of their fighters had already slipped into Europe. Experts have questioned the extent of the threat posed by ISIS and have encouraged European countries to boost their security and enhance the processing of refugees without allowing fear to influence wider policy.

Germany announced earlier this month that it had temporarily closed its borders to better manage refugee registration. Germany has also pushed for other EU member states to accept more refugees.