The European Commission building in Brussels was among possible terrorist targets for jihadist fighters returning from Syria, according to reports this weekend.
The Dutch public broadcaster NOS has said two people arrested by the Belgian authorities were planning to attack the headquarters.
The Commission said it was aware of the reports.
A Belgian broadcaster said according to several sources, a jihadist group was detained in Antwerp this summer. Their preparations for an attack were said to have been well advanced.
An attack last May on a Jewish museum in Brussels has heightened alert.
“It proves sufficiently that, after the attack that happened in Brussels, those who are in Syria – we’re talking of 4,000 to 5,000 people coming from Europe’s Schengen area – represent an imminent danger to public order in Europe and our country,” said the Mayor of Antwerp, Bart De Wever.
The French suspect being held in Belgium over the Jewish museum attack in which four people died had spent more than a year fighting with Islamist extremists in Syria.
A Belgian newspaper says the authorities have made several arrests in pre-emptive operations.
Officials have not given details but have confirmed that operations have been carried out.
