Frankfurt's customs office said Wednesday's operation code-named "Cumulus" had focused on suspected organized crime and had been requested by state prosecutors in nearby Darmstadt.

Police special commandos raided an apartment in Rüsselsheim, near Europe's third-busiest airport, which handles large volumes of international cargo, the customs office said..

At least four main suspects had been arrested, according the German news agency DPA.

Losses run into millions

Potential charges included the illegal hiring of workers, tax evasion and failure to forward pay packet social welfare deductions to authorities, it said.

Losses to state coffers amounted to at least 17.6 million euros ($19.7 million), said a customs spokeswoman.

Lufthansa Cargo said one of the premises searched was a subsidiary which had ended cooperation with a suspect firm in 2013.

The raids coincided with court proceedings in Frankfurt over alleged bribes paid during the construction of a freight center.

Europe's largest cargo hub

Frankfurt's operator Fraport describes the airport as "Europe’s largest cargo hub" with 225 scheduled cargo flights a week provided by 24 airlines specializing in airfreight.

The sprawling airport's two main cargo centers also house freight forwarders, cargo handlers, and other companies providing logistical and transport services.

ipj/msh (dpa, Reuters, AFP)