THE HAGUE, Netherlands (AP) — Seven men suspected of planning a major extremist attack in the Netherlands are scheduled to appear before an investigating judge, a day after prosecutors said that a huge police operation had thwarted their plot.

Some 400 police took part in raids Thursday that led to the arrest of the men aged from 21 to 34. Three of them, including the alleged ring leader, a 34-year-old Iraqi, have previously been convicted of attempting to travel overseas to join extremist networks.

Prosecutors are expected to use Friday's behind-closed-doors hearing to request an extension to the suspects' detention while investigations continue.

Prosecutors say the group wanted to attack a large event using bomb vests and assault rifles, and planned to detonate a car bomb at another location.

The suspects' identities have not been released.