Belgian police have arrested seven people on suspicion of preparing a terrorist attack, the prosecutor’s office said on Thursday.

The suspects had discussed several scenarios for an attack in Belgium but had not yet decided on the target, the statement said as well.

“There was talk of the NATO buildings, but at the moment those plans didn’t seem very concrete,” a spokesperson told Belgian newspaper De Standaard.

The prosecutor’s office did not immediately respond to a request for comment.

Almost all of the suspects are of Chechen origin while three are also Belgian nationals and belong to a group of fervent Islamic State supporters, according to the prosecutor’s statement.

An investigating judge will decide at a later stage if the suspects will be brought before the court.