BRUSSELS (AP) — The office of Belgium's federal prosecutor says two underage people suspected of plotting what it called a terror attack have been arrested.

Aged 16 and 17, they were arrested on Oct. 31 following raids in the cities of Eupen and La Calamine, located in the province of Liege. The prosecutor's office said they are suspected of “attempted terrorist assassination and participation in a terrorist organization."

The two minors have been placed in a youth protection center.

According to Belgian broadcaster RTBF, the two suspects had recorded a video of allegiance to the Islamic State group and are suspected of planning a stabbing attack against police officers.

The arrests were made before Monday's attack in Vienna, where a man who had previously tried to join IS went on a rampage in the Austrian capital and fatally shot four people before he was killed by police.

Four years ago, coordinated attacks killed 32 people and injured hundreds more at Brussels Zaventem airport and on the city's metro system. Belgian authorities have since thwarted several terror plots.