The RCMP and other police forces arrested 15 people Monday in a series of raids in Montreal and Toronto targeting what investigators say is an extensive international money laundering network with ties to organized crime.

The RCMP, working with the Canada Revenue Agency, began the probe dubbed "Collector" in 2016 and wrapped it up last spring before launching raids Monday at around 6 a.m. More than 300 RCMP officers in Ontario and Quebec took part in Monday's operation, aided by officers from the Montreal, Laval and Toronto police forces.

RCMP Cpl. Genevieve Byrne said the raids -- which involved 11 search warrants in Montreal and Toronto -- were ongoing and would likely continue throughout the day. Byrne said the warrants target 19 people, but only 15 had been arrested by early afternoon. The location of the four others remains unknown, she said.

RCMP Sgt. Luc Thibault said Monday's operation "targets individuals who facilitated the collection of money from criminal groups in Montreal and laundered the proceeds of their illicit activities." He said in an interview that most of the money was drug-related but would not give details about the network's operations.

Thibault also declined to say what other countries were involved in the network or where the allegedly laundered money ended up. The RCMP are planning a news conference in Montreal Tuesday morning.

Thibault said the suspects arrested Monday would be transported for detention in Laval, just north of Montreal. An RCMP plane landed around 10:15 a.m. at the St-Hubert airport in the Montreal suburb of Longueuil carrying several suspects arrested in the Toronto area. The remaining people arrested in Ontario were expected to be brought to Laval later in the day.

Police seized large quantities of drugs and $1.7 million in Canadian and foreign currency. Thibault said the Canada Revenue Agency seized properties "owned by network members" valued at $15 million.

The RCMP is not releasing the names of the suspects arrested Monday but said they will likely face charges including conspiracy, trafficking and laundering the proceeds of crime.

Byrne said the 15 arrested suspects will appear in court Monday or Tuesday in the Montreal area.