Dutch police detained 20 people Wednesday, 14 of them members of the Bandidos motorcycle gang, and seized weapons including five rocket-propelled grenade launchers and six automatic handguns.
The discoveries came in a coordinated series of raids involving riot police, specialist arrest squads and a police helicopter that targeted 30 locations in the southern Netherlands and also spread into neighboring Belgium and Germany.
Maastricht Mayor Onno Hoes said police "took tough action that was absolutely necessary to restore public order" in a region that has been plagued in recent months by violence blamed on rival motorcycle gangs.
Police and prosecutors said that members of motorcycle gangs are "heavily involved in criminal ... activity in the areas of weapons, drugs and intimidation."
The 19 men and one woman detained Wednesday are suspected of crimes including drug trafficking, extortion and money laundering, prosecutor Roger Bos said at a news conference.
As well as the weapons and large amounts of ammunition, police uncovered a drug laboratory, chemicals used to make synthetic drugs, counterfeit money, stolen cars and a cannabis plantation, Limburg police chief Gery Veldhuis said.
Members of the Bandidos gang were involved in a shootout earlier this month in Waco, Texas, that left nine people dead. U.S. authorities said the shooting began during an apparent confrontation between the Bandidos and the rival Cossacks gang.
There was no indication that Wednesday's raids in the Netherlands were linked to the Texas shootings.