Belgian, French and Swiss police conducted a series of raids and arrested 31 suspects in connection with February's major diamond robbery from a plane set to leave Brussels Airport.

Belgian prosecutor Anja Bijnens said at a news conference that one person was arrested in France, six in Switzerland and a further 24 in Belgium.

A suspected member of the eight-man gang, who posed as armed police and seized the stones from the cargo hold of a passenger plane on the runway, was picked up in France on Tuesday. This was apparently the catalyst for further mobilization.

"The probe led to a big police operation yesterday," a spokesman for the Brussels prosecutor's office, Jean-Marc Meilleur, said on Wednesday. Subsequent early morning raids involved more than 200 Belgian police officers and "recovered big amounts of cash," he said.

His colleague Bijnens said that as well as the seizure of currency in Belgium, some of the diamonds were recovered in Switzerland, neither of them went into detail on the amounts.

The Antwerp World Diamond Center had estimated the value of the gems stolen on February 18 at $50 million (38.1 million euros). The northern Belgian city of Antwerp is one of the world's key diamond hubs.

The group of eight men had cut a hole in a fence at the Zavantem airport in Brussels. They drove through in imitation police vehicles with flashing sirens and themselves wore mock police uniforms and masks. The armed men then snatched 120 parcels from a diamond shipment that was being loaded from a security truck onto a plane bound for Switzerland.

The apparently professional band made it in and out within minutes and never fired a shot.

Prosecutor Meilleur said the man initially arrested in France was thought to be among the airport robbers.

"This person has a very heavy judicial background in France and his extradition to Belgium has been requested," Meilleur said.

msh/jm (AFP, AP, dpa, Reuters)