Prosecutors said there were no indications that the suspects had already chosen a specific target. They declined to give further information.
The house searches took place in the cities of Antwerp, Liege and Ghent, among others, and in the Brussels region.
“The asylum procedure is for those fleeing war or unjust persecution. There is no place for people who pose a danger to society," said Belgian Immigration Minister.
"Escalate for Palestine, everyone," the graffiti on the Monument to the Righteous of Belgium read.
Israel's war in Gaza has sparked global demonstrations, including in Belgium, where pro-Palestinian activists have organized protests and sit-ins at universities.
The memorial plaque in Brussels that a white swastika and the white nationalist version of the Celtic Cross had been painted on the memorial.
The university will continue its research projects with six non-academic Israeli institutions, saying they could not find any links between them and human rights violations.
Israel’s spy agency charged that Iran was behind the grenade attack against Israel’s Embassy in Belgium this past weekend.
Brussels sanitation workers chant death threats against Jewish politician Viviane Teitelbaum. Complaint filed, disciplinary action pursued.
While police have not announced a motive, this is one of many incidents this week against Israeli embassies across the globe.