Brussels: Belgian police have received an alert that a group of Islamic State fighters recently left Syria en route for Europe planning attacks in Belgium and France, according to a Belgian security source.

The Belgian crisis centre in charge of coordinating security responses confirmed that an alert had been circulated to all police forces in the country but there were no immediate plans to raise the security level to the maximum that would indicate an imminent threat of an attack.

Observing a one minute silence at the Place De La Bourse in honour of the victims of the terror attacks in Brussels in March. Credit:Getty Images

A source at France's Interior Ministry said Belgian authorities had transmitted a note to their French counterparts, who were currently reviewing the information in the alert. "We know the threat is very high", the source said. "We're reviewing all the elements (in the alert)."