Authorities have charged two Belgians with terror-related offences in connection with an attack two years ago on a high-speed train in northern France that was foiled by three Americans.

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 U.S. military members.

French police called it an Islamic extremist attack.