Police in Belgium arrested seven people Thursday on suspicion they were preparing a "terrorist attack", federal prosecutors said, adding that 14 raids were conducted nationwide.

A spokesman for the prosecutors' service said there was no evidence at this stage of any link to the 2024 Paris Olympics, whose opening ceremony takes place on Friday under unprecedented security.

There are "no details at this time as to the locations or targets but what was found leads us to believe an attack was being prepared," the spokesman, Arnaud d'Oultremont, told AFP.

The suspects arrested were to appear in court Thursday before the anti-terrorist judge who ordered the raids to determine whether they would remain in custody or not, the prosecution service said in a statement.

It said all of them "are suspected of participation in a terrorist group's activities, financing of terrorism and preparation of a terrorist attack".

Thursday's police raids across Belgium were carried out in Brussels, Antwerp, Liege, Courtrai and Menin, under warrants issued by the Antwerp-based judge, the statement said

Prosecutors said they were releasing no other information at this point.

Belgium in 2016 was rocked by suicide bomb attacks at its airport and in its metro system that killed 32 people and wounded hundreds. 

They came a year after attacks in Paris in which 130 people were killed.

The attacks in both countries were claimed by the Islamic State group. The only surviving member of the jihadist cell that carried out the Paris attacks, Belgian-born French citizen Salah Abdeslam, was last year also convicted of involvement in the Brussels attacks.

In October last year, a gunman who said on social media he was inspired by the Islamic State group shot dead two Swedish football fans in Brussels. 

Police tracked down and the next day killed the shooter, Tunisian national Abdesalem Lassoued, in a confrontation.