“An international organized crime network responsible for the large-scale production and trafficking of synthetic drugs has been broken up following an extensive investigation," Europol said in a statement issued in The Hague.
"The operation resulted in the arrest of its key members, the discovery of three illegal drug production facilities and the seizure of over 100 kilogrammes of amphetamine...firearms and explosives," it said.
"Operation Fire" was launched in March in cooperation with police in several EU countries, including Sweden and Germany, after Swedish police noticed an increase in amphetamines being smuggled into the country.
Around half of the seized amphetamines were confiscated in Sweden following raids by customs officials in Malmö.
Europol said it helped with the exchange of information in various countries.
"During the operational phase of the investigation, 30 kilogrammes of amphetamines were seized and three people arrested in Sweden as well as two in Germany and one in the Netherlands," Europol said.
Two people are now facing charges on suspicions of aggravated drugs offences, narcotics smuggling, as well as weapons violations.
“We also found weapons during our raids,” Eveline Bomark of the Swedish customs agency (Tullverket) told the TT news agency.
Three suspects were arrested in Bulgaria, where police destroyed an equal number of drug-making facilities. They seized five guns, 150 rounds of ammunition and 6.4 kilogrammes of TNT explosive.
They also confiscated 75 litres of amphetamine base, enough to make 120 kilogrammes of pure amphetamine, 15 kilogrammes of amphetamine and over 1,400 litres of various chemicals to make synthetic drugs.
Europol's director Rob Wainwright called the operation "a major blow against this dangerous criminal network", while Swedish EU Home Affairs commissioner Cecilia Malmström tweeted it a "good day for police cooperation" on social networking site Twitter.
"The joint operation goes to show just how immensely important it is for national law enforcement and Europol to effectively exchange information about dangerous criminal activities," she added in the Europol statement.