Germany’s population of Islamic extremists has grown from 100 people in 2013 to 1,600 in the last four years, the country’s security and intelligence agency (BfV) announced Wednesday.

BfV said that radical adherents increased by several hundred in recent months. Out of the 1,600 on the list, about 570 are considered “dangerous” and capable of plotting a terror attack.

“We receive between two and four credible tips on planned terrorist activity in Germany each day,” BfV chief Hans-Georg Maassen said, according to Deutsche Welle (DW). “We have to recognize that we are living in a different situation now than was normal.”

Officials attribute the rapid growth to how easy it is to connect with extremists online, along with press coverage of terror plots and attacks.

“These are social groups that find each other, let’s say through their mosque community, and the people who see them in the real world don’t necessarily notice any change in behavior,” Maassen told DW.

The number of Salafists, or fundamentalist Sunni Muslims, have also increased at a rapid pace — from 3,800 in 2011 to 9,700, as of January. Authorities shut down several Salafist mosques in recent months since they consider the movement to be a gateway to radicalization.

“It’s of great concern to us that this scene is not only growing, but it is also very diversified. There is not just one, two, three or four people who have a say,” Maassen warned in January. “Rather, there are many people who dominate this Salafist scene. And all these people have to be watched.”

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