The police operations that took place in the Brussels area late Sunday have ended, a source close to the authorities said, as the Belgian capital remained on the highest security alert level over fears of a Paris-style attack.

The federal prosecutor will hold a press conference at midnight (2300 GMT) to discuss the latest developments, the source told AFP, without giving further details.

The police had earlier called for a social media blackout during the operations so as not to give away officers' movements.