Guns, munitions and explosives, as well as police uniforms and a large amount of money, were seized by police. Eric Van Der Sypt, an official at the prosecutors' office, told AFP that: "The investigation ... has shown that these people had the intention to kill several policemen in the street and at police commissariats [police stations]."
Thirteen people were arrested but only five would be prosecuted, he said. Belgium would also seek the extradition of two suspects held in France.
The Belgian Government has also announced new measures to deal with terrorist suspects.
They include making travelling abroad for terrorist activities a crime and expanding the cases where Belgian citizenship can be revoked for dual nationals thought to pose a terror risk.
No link has been established between the terrorist plot in Belgium and last week's Paris attacks.
But French Prime Minister Manuel Valls said both countries faced the same threats. "The link that exists is the will to attack our values," he said.
Twelve suspects are being held by police in the Paris region over the attacks that killed 17 people.
Police carried out raids in five towns, iTele reported. Those arrested are being questioned about "possible logistical support", such as weapons or vehicles, they could have given the three gunmen.
France remains on its highest terrorism alert level and authorities have said 120,000 police and soldiers have been mobilised across France.
The incidents in France and Belgium have impacted on their European neighbours. Spain has launched an investigation into the visit of gunman Amedy Coulibaly to Madrid days before the Paris attacks.
Police in Germany have also arrested two men following raids on 11 properties. One of the men was suspected of leading an extremist group of Turkish and Russian nationals.
Police said the group was preparing a serious act of violence in Syria but that there was "no indication" that the group had been planning attacks in Germany.
British police have been warned a terror attack against them is highly likely.
Europol head Rob Wainwright told the BBC World Service the need for tightened security across Europe highlighted the complex nature of the terrorist threat.
"We're dealing with multiple thousands of potential terrorists."
He said it was hard for police to identify plans because suspects were "working in a self-radicalised way very often, not necessarily under any command and control structure".
