Police arrested four suspects this weekend over what Belgium's justice minister described as a plan to kidnap him.

Vincent Van Quickenborne, who is also mayor of the city of Kortrijk, in western Flanders, appeared to blame a "drug mafia" in a video message run by state broadcaster RTBF.

Addressing an audience at a local ball, he said that in a phone call on Thursday, a federal prosecutor had warned him of a kidnap plan targeting him.

On Saturday, federal prosecutors said police had beefed up security for Van Quickenborne, citing a serious "threat".

They said three people had been detained in The Netherlands and that Belgian authorities were seeking their extradition.

A spokesman for the Dutch prosecutor's office in The Hague said the trio, all Dutch, were aged 20, 29 and 48.

On Sunday, a judicial source said a fourth suspect had been arrested in The Netherlands.

Following a report in the Flemish daily Het Laatste Nieuws, the source confirmed to AFP that an automatic weapon had been found in a vehicle spotted near the minister's home in Kortrijk.

On Saturday, Van Quickenborne tweeted: "My family and I are safe. Our fight against organised crime continues. With greater manpower and more resources than ever. We shall never bow to violence."

The prosecutor's office said it had been "informed last week of a possible threat" which led to an investigation. It would not provide further details.