Brussels could be a target for terrorists during the month of Ramadan as security is beefed up in crowded public places, such as fan parks showing Euro 2016 matches.
Schools and hospitals are being closely monitored as well.
Information from security services on the possible terror threats was reported in Dutch newspaper Het Laatste Nieuws.
The attacks could take place during Ramadan – the Muslim month of fasting – which started on June 6 and will last until July 5.
Last month ISIS released a chilling video calling for attacks on Europe and the US during the holy month.
In a recording titled ‘That They Live By Proof’ the group’s spokesman Abu Mohamed al-Adnani said: ‘Ramadan, the month of conquest and jihad. Get prepared, be ready…to make it a month of calamity everywhere for the non-believers…especially for the fighters and supporters of the caliphate in Europe and America.
‘The smallest action you do in their heartland is better and more enduring to us than what you would if you were with us. If one of you hoped to reach the Islamic State, we wish we were in your place to punish the Crusaders day and night.’
Belgium has been on high alert after coordinated suicide bombings at Brussels airport and at Maalbeek metro train station, which left 35 dead and was the deadliest terrorist attack in the country’s history.
Last Friday night two police cars were torched in the working class district of Molenbeek – which is 80 per cent Muslim – and is often referred to as a ‘hotbed for Islamic extremism’.
Belgium – which has a population of 11 million people – has supplied the highest per capita number of fighters to Syria of any European country.