Police in Germany have conducted raids across the country over an alleged plot by suspected militants of Chechen origin to launch a violent attack, Berlin prosecutors say.

On suspicion of planning a serious violent act endangering the state, search warrants are being executed in Berlin, Brandenburg, North Rhine-Westphalia and Thuringia, the Berlin attorney general’s office said in a tweet on Tuesday.

It later said that the investigation targeted militants of Chechen origin.

It was not clear how many individuals were arrested.

Over the past few years, Germany has suffered several attacks of terrorist nature both from elements of its far-right, nationalist groups and people believed to have links to the Takfiri Daesh terrorist group.

The deadliest such attack took place in 2016 when a Tunisian man stole a truck and drove it into a Berlin Christmas market, killing 12 people.

In April, the Office for the Protection of the Constitution, Germany’s domestic security watchdog, warned of an increased risk posed by homegrown Daesh militants returning from Syria and northern Iraq. Its director, Thomas Haldenwang, said that an estimated 2,240 such militants with terrorist potential were living in Germany.

Extremists from across Europe joined Daesh in 2014, when the terrorist group launched offensives in Iraq and Syria. While the European governments took no action to stop the militants from traveling to the two Middle Eastern countries, they are now facing potential risks from their return.