BERLIN (AP) — Prosecutors say authorities have searched eight apartments across Germany and temporarily detained six Syrian men who are accused of preparing a terror attack.

Frankfurt prosecutors wrote in a statement that 500 police officers searched buildings early Tuesday in the cities of Kassel, Hannover, Essen and Leipzig.

The six suspects were identified as Syrian citizens aged between 20 and 28 who arrived in Germany as asylum-seekers between December 2014 and September 2015. Their names were withheld as is customary in Germany.

The men, who are allegedly members of the extremist Islamic State group, are accused of "having prepared an attack with weapons and explosives on a public target in Germany."

Prosecutors refused to give further details, citing the ongoing investigation, but said the men had not yet finished preparing their attack.