Belgium's Federal Prosecutor's Office said Tuesday that one suspect, identified as Mohamed B, was accused of leading a terrorist group and the other, Youssef S, of being part of it.
Authorities said no arms or explosives were found during six searches on Monday but four people were detained. Two were released after questioning.
In August 2015, a man with an assault rifle tried to open fire on a Thalys train that had just crossed into France from Belgium but was overpowered by three Americans, two of them off-duty US military members.