BRUSSELS, March 28 -- Three of the nine people arrested in police raids Sunday were charged with participation in a terrorist group, the Belgian broadcaster RTBF reported Monday.

The three people were identified as Yassin A., Mohamed B. and Abubaker O., for whom the Brussels investigating judge has already issued arrest warrants.

Belgian federal prosecutor gave no additional information regarding the investigation.

According to RTBF, the three people were believed to be involved in a new case, which was neither related to the Brussels explosions last week nor Paris attacks in November last year.

The Belgian federal prosecutors confirmed in a statement on Sunday 13 raids took place in Belgium in the morning as part of an investigation against terrorism. Nine people were arrested, and six of them were released.