Greek authorities have seized nearly two tonnes of cannabis during an operation to dismantle an international ring of Greek and Albanian drug dealers in Attica and Larissa, during which they placed six suspects under arrest.

The raid was carried out on Saturday by the Attica Security drugs squad, working in collaboration with the Attica financial crimes unit (SDOE) drugs department and the U.S. Embassy's Drug Enforcement Administration bureau.

They arrested one Albanian and five Greeks, including the suspected mastermind of the ring, who were in the process of transporting the drugs to western Europe using long-haul trucks for international transport.

The police operation was based on a tip-off about the ring's activities and a three-month investigation that led detectives to the ring's mastermind, who owned a trucking company and other businesses in Larissa, and one of his closest associates.

The two were placed under close surveillance, leading police to a large warehouse in the industrial region of Aspropyrgos Attica that contained tools and equipment for converting trucks in order to make special crypts in the floor or roof that could be used to carry drugs.

Investigators also discovered that the suspects were preparing to export a large quantity of cannabis to England and traced the trucks that would be used for this purpose.

The police operation was carried out on Saturday, leading to the seizure of two trucks containing one tonne and 200 kilos of cannabis. A further 620 kilos of cannabis were found in the Aspropyrgos warehouse, where they were being guarded by an Albanian armed with a Kalashnikov rifle.

As well as the owner of the trucks and the Albanian, police also arrested three truck drivers and a man that had leased the Aspropyrgos warehouse. They confiscated the drugs, three trucks, the Albanian guard's Kalashnikov and a clip of bullets, a private car, 32,455 euro, 1,125 GBP, 80 Scottish pounds, 12 mobile phones and four precision scales.

Under questioning the suspects have admitted to at least two more shipments of cannabis to England using trucks in February 2011, while police are now focusing on the group's economic activities to discover incidents of money-laundering.

All six arrested were led before a public prosecutor on Sunday, while an investigation is continuing to arrest yet more of their accomplices.