September 13, 2016 8:26 AM EDT

Reuters reported, citing federal prosecutors.

Police seized “extensive material” in the pre-dawn raids in Schleswig-Holstein and Lower Saxony that led to their arrest, BBC News reported.

The suspects—aged 17,18 and 26—traveled through Turkey and Greece to get to Germany, using passports, cell phones and $1,000 in cash provided by ISIS, Reuters reported. Investigators have not yet discovered details about a specific attack plan.

The arrests come as Germany continues to reckon with a refugee crisis. More than a million migrants arrived in the country last year seeking asylum. German Chancellor Angela Merkel has refused to limit the number of refugees allowed into the country, though she has faced pressure to do so, especially in the wake of several violent attacks in July, some of which were carried out by refugees.

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Write to Katie Reilly at Katie.Reilly@time.com.

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